It’s not an obsession, it’s probably because Doom is easy to understand from a code perspective, and also addresses a lot of graphical/game code techniques, aka its a perfect hobby from a coding perspective to learn, adapt and tweak. It’s actually the perfect example of Hacking.

Also this hacking started early on, so there is probably tons and tons of documentation and data, again making it a great candidate to work with it from a hacking perspective.