Homebrewing is difficult work. I'm the kind of person who likes not only to understand the rules, but also the reasoning behind the rules before I alter or amend them myself.
However, as I've discovered recently, finding sources that explain said reasoning is really difficult. Google shows a multitude of useless results for any sort of thing resembling a developer commentary. My go-to resource for these things, this site, has designer-reasoning questions declared off-topic (yet I'm still asking here). I never get answers on Reddit.
Throughout the process of asking this question, I've learned a few things. The original question (Have WoTC ever made a designer commentary) has basically been answered (they have). However, they also decided to disappear said commentary along with lots of community dialogue, presumably leading to the difficulty I am having.
Therefore, I ask: Where is a good source that I can find official designer commentaries that explain the reasoning behind the rules of D&D 5th edition? Note that this is distinct from things from Sage Advice. While that clarifies various rules, I'm looking for developer insight into the construction of the rules.