It's Doom in part because it's a significantly popular game, that was open sourced, with low resource requirements (but not too low to be trivial), with an inn

It's Doom in part because it's a significantly popular game, that was open sourced, with low resource requirements (but not too low to be trivial), with an innovative custom engine that people find interesting, originally created by a person who many respect or admired growing up, and the game itself is cool. And now there is enough inertia to keep choosing it.