"Where's Emacs or Vim of game engines which brings its own unique philosophy?"
All forgotten in obscurity.
When making a game, people are usually not so much interested in the philosophy of their tools, but shipping things with it as soon as possible.
That means working as expected.
And then the forums and subreddits are flooded with miserable folks complaining about how destructive, inextensible and unpleasant to use those experiences are. This is not the problem of UI in engines itself, it's problem of how long it takes to bring it to acceptable state with all those moving parts. For UE, Unity and Blender it took decades.
Complaining is a lot easier than actually doing anything.
Realise that the people you are slinging mud at are actually busting their asses to provide game engines to the public some of them for free and with the source.
To be honest for most developers editors are much alike. While Emacs and Vim guys debate on their philosophies and config files others just open their favourite editor/IDE and ship.
Lol, I haven't tinkered with my emacs config in nearly 10 years now. Most vim and emacs users put together a config they like over maybe a few weekends then get to work. We have deadlines to meet just like all the rest of you.
This take has given me second degree burns. I must have never shipped anything then, what with vim being my favorite editor.