I guess people wants more than a CRUD. With Pages you won’t be able, for example, to use Commerce (to charge for submissions or access), use Clubs, use extensions (from other apps and some from Core too), among several other things. I remember these from the top of my head but probably there are more.
I mean, you probably could do it with Pages if you hook here and there, etc. But why, if you can do this easily with an app?