It is weird our fanbase at the moment. I do think a certain level of apathy has developed as fans are now so used to success. Strange example but last year we couldn't fill the academy stadium for the youth cup final yet 10 years about 20k turned up for when we beat chelsea. You then look at games like Hamburg and Newcastle in 2004 when where the Etihad was filled to the brim and extremely hostile. You don't see that anymore.
Cost is certainly a major reason and probably why I wont be going to the Barce game.
Also while the club has tried to improve the 'match day experience' it has certainly sanitised the experience which i'm sure has put of a lot of the old hard core. Probably the biggest reason why the crowds are so poor in cups imo
The home gates in the FA cup are actually really impressive and have been in the last 4 or 5 years sell outs or very close.