Something I've noticed about software dev vs game design: software is better (easier to read, understand, maintain, etc) when you have clean, separated modules. Game design is better (more fun) when everything is connected (eg in an fps, everything relates to gunplay, damage systems, environmental destruction, in a building game, everything relates to building, the building ui, inventory, resources etc). I think this mismatch shows up in game code.

Combine that with actual hard performance constraints, and if you're a "normal" software dev casually browsing some game code, it can be shocking (eg Celeste movement code: https://github.com/NoelFB/Celeste/blob/master/Source/Player/...).