WOW has diminished so badly because:

1) they DIDNT cater enough to casuals
2) Ion is a lawyer not a game developer and it shows!
3) developers inflated egos versus good game decisions
4) they have been charged with a disgusting amount of law suits for sexual misconduct discrimination etc

many many reasons why wow is a state of decline , it never has been and never will be related to casual vs hardcore.

open your eyes please