It's absolutely possible for unity games to have stunning visual.
The problem, like others pointed at, is that it is more used with Indie than AAA.
From my experience 3 main issue come to mind as to why that is. (this maybe a little dated mind you)
1) Unity have frequent update which add/update/remove feature which does not help for stability. So if you develop an AAA stability of the engine is important.
2) The way unity save scenes is not trivial to use with source control and merge tool for code sharing.
3) Unity use C# (which is awesome) but the vast majority of AAA dev still use C++/Unreal. Even tough C# is way more user friendly and readable than C++/unreal dev teams skills and experience would have to completely be renewed which would be both costly and time consumming.







