Obligatory: I am playing in a campaign I made myself using homebrewed rules based on a German pen-and-paper RPG called Das Schwarze Auge (DSA; The Dark Eye in English).
I am a GM for a group of around 5 players, who meet every 1-2 weeks. We play for a few months already, but I am a little dissatisfied with the current situation for a few separate reasons. One of them is that my players don't immerse in my World as I would like them to.
My style of storytelling conflicts with the way my players react to the world. I don't want to have a dead-serious Pen&Paper game, but I'd like to craft a 'semi-realistic' world for my players to explore. I put a lot of effort into Characters and Worldbuilding, create long and detailed questlines and create different intertwining plots and events. I even got one of my friends from outside of the group to play a villain, who is already plotting and influencing current adventures, without my group even knowing about him yet. My players, however don't seem to appreciate my effort at all.
They act like Players rather than like Characters. In a video game like Skyrim, there is no moral codex for you to follow and neither are there any real consequences (but a measly fine, that even allows mass murderers to simply go free for a few coins). From the viewpoint of a player, there isn't really any reason not to just steal this valuable dragon claw from the Riverwood Trader as soon as returned it. The quest is done, the item will simply lie there for all of eternity and the game won't change if it vanishes - heck, the shopkeeper wouldn't even notice. A few of my players don't seem to understand that doing something in my world will have a ton of consequences not just for them, but for everyone involved. Worst of all is our Paladin - paragon of virtue - who previously played a cutthroat assassin and now plays basically the same character in shiny armor (although he really cares about his image - which means he never leaves witnesses...).
They completely disregard NPCs' lives. I already made posts about my murderhobos here and followed an advice to make them feel consequences. After I did that they became rather crafty, and stopped killing people in plain sight, but everyone who 'disrespects' them (no matter whether it is a snobby knight or simply a trader who didn't have favorable prices) will have their lives mysteriously shortened quite soon. And they really take care about any loose strings now. They also don't take any prisoners, use their NPC companions simply as replaceable baits and don't even consider any other option to solve conflicts but violence. Not everyone in my Party is like this, but the rather moderate part of the group will issue a quiet verbal objection at best. I don't even have a problem with 'evil' characters per se, but not only is there quite a large disparity between evil and good in my group, but these ruthless actions also frequently interrupt my plot, which became quite a nuisance to deal with for me.
Even though they already are in the same region for over 10 (almost weekly) sessions, most of them still struggle to remember a single thing, whether it might be a NPC, a town, a village a tavern or even their very quest. It is hard to form any relationship with a person you neither remember nor ever asked for their name, despite being on a escort quest for several sessions.
Some additional Information:
I don't use any alignment system (I haven't seen one in default DSA yet either). My players seem to mostly play themselves with a few varying quirks and fighting styles anyways. I don't think they can abide an alignment on their own and I don't want to enforce/restrict their actions permanently.
Since I already wrote my completely own character sheet generator and rules, abolishing most of basic DSA, working with the rules won't work. I am open for interesting concepts, but again don't want to enforce anything, as my group kinda expects that I'll bend any rule they disagree with to their liking anyway.
I already tried a few things to solve these problems:
I tried to give NPCs better motivation, quirks and backstories, but my group is superficial, forgetful and quick to judge. They don't care about interacting with NPCs any more than necessary to make this worth the effort.
I talked with my players. This seems to be treated as some kind of panacea on this site. I actually talk with them a lot, although mostly they forget any good resolutions I talked into them about halfway through a session, which is, why I am explicitly looking for way to improve myself here. Creating an even more immersive world, will make it easier for my players to immerse in it - at least that's my plan.
edit: Since this was asked quite a few times now: When i talked to them they reacted quite different. Most understood my problem, but - even after a lot of talking - offered no idea as how I can help them to treat NPCs and their belongings with a little more respect. One got convinced that giving the NPCs more personlity will make them overshadow the group (like solving your own riddles with a GMPC), which wasn't really my intention, but I eventually gave up argueing. Another one simply told me, that "NPCs are never as important as players" over and over again, which again wasn't what I wanted. I'd just like their characters to treat NPCs like actual living beings, rather than as a resource you can waste, simular to gold in a tavern, no matter what's their stance on NPCs as players.
I had them feel consequences. One of my character wanted to play a mage, who draws power from a demon within him, who grows stronger whenever he takes damage, and then has gotten his ass beaten in each combat since, so they demon took over his body and my group had to go to the shadow realm to rescue their buddy and banish the demon, losing one of their characters on the way. They got an important NPC killed some time ago and I still have others NPCs remind them 'If only XYZ was here, he'd know what to do'. They were on trial for murder and robbery twice already, with one character banished from a city and one facing a life long imprisonment. They lost a lot of NPC companions along they way and now have to face an enemy with a numerical advantage. They also mostly accept my 'punishment', but just stumble into the next disaster right away. They derailed my original plot in session 3 (of ~12) and are ever since moving in a downward spiral, causing even more problems, before they manage to solve an old one. It is agonizing to come up logical reasons to avoid a TPK every time. It feels like I am only telling 'their story' rather than 'mine'.
We took inspiration from another Question here and now write a Log, but during sessions it is rarely used.
In what ways can I encourage my group to consider my game world from the perspective of their characters, rather than from the perspective of a player, in order to have them care more about their environment?