@enigmatico outside of convenience and marketing, I feel like space might be a reason as well. a proper gaming PC usually calls for a dedicated desk and chair, which can take a decent chunk of space. along with the hassle of setup, especially if the user is unfamiliar with PC gaming, a console can just be tucked away in an entertainment center without taking up additional space.
PCs dont require a "specialized chair". If you want to use mouse and keyboard, just get an office chair. If you want to play with a pad, you can just sit in your couch while playing. Steam has the "big picture" mode which lets you use the steam interface with a game pad. Not to mention that Windows integrates a game interface as well. Get an xbox controller, press the xbox button, and the interface pops up.
As for space, I'd say the PS5 is pretty bulky by itself. The series X, not so much. Still, a MicroATX can do fine for mid-range GPUs and its not any bigger or heavier than a PS5. Any B450 mobo will work for this. However, have in mind that the bigger the case, the better the airflow will be. And we all know how "good" the cooling in those modern consoles is.
PCs dont require a "specialized chair". If you want to use mouse and keyboard, just get an office chair. If you want to play with a pad, you can just sit in your couch while playing. Steam has the "big picture" mode which lets you use the steam interface with a game pad. Not to mention that Windows integrates a game interface...