Post Second Sundering, what keeps evil gods from defecting from the new paradigm of non-interference?

Question

In 5th Edition Forgotten Realms, the designers' intent is that the gods have withdrawn from the world and for the most part leave mortals to make their own fate - Matt Sernett and Chris Perkins talk about this in the Dragon Talk podcast from December 2016 (episode 'David Eddings on Roleplaying Claptrap', after the 8th minute):

the Sundering is really a statement about where we want to take the Realms going forward, which is: the gods are around but at the end of the Sundering they withdraw from the world to an extent and basically usher in what could be considered an age of mortals, where the fate and future of the world will be decided by the people in it, not by the gods.

It may make sense for good or neutral gods to withdraw from the Realms to leave mortals with more self-determination, but what incentive would the evil gods have to do so? And if there is no incentive, won't their sustained interference force the good/neutral gods to return to interfering in the Realms just to maintain balance?

I'm looking for a canonical answer to this question, from published materials or designer statements.

Answer 1

Ao created tablets of new rules intended to restore peace and balance to Toril.

In a video of a 2012 Gencon panel featuring Forgotten Realms novel authors, What is the Sundering (Part 1), it is stated that the supreme overgod Ao intentionally re-created the tablet of rules that separated the worlds of Abeir and Toril, intended to restore balance and order to Toril.

The events of the D&D 4th edition era where the now twin worlds of Abeir and Toril were recombined into one world are revealed to be the result of Ao destroying tablets of rules he created, those that divided the worlds in the first place long ago. Originally, their purpose was to divide the world into Abeir, where the Primoridials held sway, and Toril, where the Gods had power.

However, when two deities stole the tablets and began fighting amongst each other, Ao destroyed them to teach the gods a lesson, and the worlds were recombined. Unfortunately, this only made things worse, and so Ao set about recreating the tablets and dividing Abeir and Toril in two once more, but this time with a new rule limiting the ability of the gods to damage Toril in their petty squabbles.

Ao's reasons are described at 11:35 in the video:

Once it is over, the word of Ao declares: The Era of Upheaval is ended. Great stories remain to be told in this era, but they are not the stories of gods and godlike beings. They are the tales of mortal heroes, taking a stand to preserve the world they love.

This ethos reflects Wizards of the Coast's policy for the focus of Realms products and novels, which we learn at 23:20 in the video is intended to return to "the heart of high fantasy", and at 31:15 it is stated that WotC wants individual characters to be significant actors (e.g. why player characters should have to save the day instead of leaving it to deities).

As such the novels of that era will focus on the actions of people, not the gods or Ao. It may be that no novel or sourcebook explicitly references this lore about Ao stated by Wizards of the Coast. At 36:48 in the video, it is said to be likely that no protagonist of these novels is likely to be fully aware of the situation with the gods, and even Elminster may only partially understand it.

It should be noted that gods can, to some extent, defy Ao. It was gods who stole the tablets from Ao in the first place, and Tiamat has a loophole which allows her to be summoned in person to Toril. This suggests that Ao's new rules are significant, but not necessarily absolute.

Answer 2

The most likely answer is that the overgod Ao dictates/requires so. There is a GenCon 2012 panel session on The Sundering, where many of the authors of the novel series of the same name are present. While it does not give a direct "Ao makes it so" statement, the overall tone, with Ao recreating the Tablets of Fate, and declaring an end to the Era of Upheaval which had started during the Time of Troubles would imply such an arrangement. The deities are expected to have learned the folly of not upholding the balance that Ao expected. Quoting (starting from around 11:40 in the video):

... the word of Ao declares the Era of Upheaval is ended. Great stories remain to be told in this new era, but they are not the stories of gods and god-like beings, they are the tales of mortal heroes, taking a stand to preserve the world they love. ...

Answer 3

Nothing really. A number of adventurers have players around or interacting with very direct and overt gods or supreme beings

https://en.wikipedia.org/wiki/The_Rise_of_Tiamat

The Rise of Tiamat, along with the previous adventure, Hoard of the Dragon Queen, pits players against Tiamat.[1]

https://en.wikipedia.org/wiki/Out_of_the_Abyss_(Dungeons_%26_Dragons)

The adventure takes place in the Underdark, and begins when the players are captured by Drow Elves. They escape with a group of other prisoners to find that demons have a stronger influence in the Underdark than expected. As they travel between locations searching for an exit from the Underdark, they discover that various demon lords including Demogorgon, Zuggtmoy, and Juiblex, have been unleashed.

And from the book.

You behold the true form of the Demon Queen of Spiders-that of a black. bloated arachnid with the head of a female drow. Nestled in the webs all around her are thousands upon thousands of gray eggs. Lolth knows she is being scried, her fury tangible as her mind reaches out to find you. Her shriek of rage as she's shut out by the powerful wards of Gravenhollow echoes in your mind as the vision is suddenly torn away to darkness.

https://www.goodreads.com/book/show/28503767-the-devil-you-know

Before Farideh took a devil’s pact, before she was Chosen by the god-king of the Hells, before any of this started, there was Bryseis Kakistos, the original Brimstone Angel, first of Farideh’s line. Now, at the end, there is also Bryseis Kakistos—but this time, instead of helping the king of the Hells achieve godhood, she’s going to kill him. All she needs is a little help from Farideh—which she should, by all accounts, be happy to give. After all, who could object to killing the king of the Hells? Except, it turns out, Farideh. Because as always, things are far more complicated than they seem.

Or to rephrase, it's entirely expected to have players have adventures which are centered around preventing the return of evil gods, or invading hell to slay gods, or interacting with god kings or other deities. Those are prominent and major plotpoints in their literature and adventurers, and gods orchestrate a lot of major events.

This is what Ao intended.

https://youtu.be/eAoq-vwWHHg?t=702

"The era of upheaval is ended. Great stories remain to be told, but they are not the stories of gods and godlike beings. They are the tales of mortal heroes, taking a stand to preserve the world they love."

So, the intent is that the stories are about mortal heroes (which may involve mortal heroes defeating gods) not about divine beings interacting among themselves. They have not done much to stop gods actually doing things, because gods make fun plot elements.