Also value-oriented builders probably wouldn't want to use the ITX form factor given they're always more expensive than mATX with a on-par feature set at best. ITX builders likely are not price conscious.
mATX cases can also be quite small (e.g. Fractal Node Define 7) but you get 2 more RAM slots, can use ATX PSU, and can get bigger coolers so not have to resort to price AIO.
mATX cases can also be quite small (e.g. Fractal Node Define 7) but you get 2 more RAM slots, can use ATX PSU, and can get bigger coolers so not have to resort to price AIO.