I think a part of it is the Instagram/Twitch mentality where publicly performing or sharing something plays into things now.

Easier to take photos of your computer and share them if they look like a cryogenic chamber. :)

In addition, a lot of companies are going "full stack" for computers, and a system-wide RGB integration/syncing for Company X's components (RAM, motherboard, graphics card, case, fan controller, fans, mouse, keyboard, mousemat(!)) is a simple way to lock in customers.

EDIT: You could also argue that we're at an inflection point where videogames and tech nerdiness are normalized to the point where computer cases, like TVs once were, are now considered furniture and not some heinous eyesore you're forced to have around.