To be a bit more charitable: I'd say that generally games involve a lot more special-casing than most code, and more planned out scripts (in the movie sense) of things happening, which tend to be antithetical to good coding practice, and encourage spaghetti, which begets more. In my experience, games that are procedural tend to be much cleaner code-wise, because they tend to fit the model of cleaner code better.

I think game engine tooling tends to encourage bad code too, lots of game engine make it hard to do everything in code, rather things are special cased through UIs or magic in the engine, which means you often can't use all the normal language features, and have to do things in awkward ways to fit the tooling.

Of course, this varies a lot by engine.