I think it started to go wrong when clubs were allowed to keep their own gates instead of sharing - suddenly teams like United had a big advantage over less well-supported clubs.
I did try supporting another team - I lived in Liverpool in 65 and thought I would give them a go. I watched two games of St John, Hunt, Yates, etc and realised that I just didn't care whether they won or lost and was missing Paine and Sydenham.