It's probably impossible to answer as an old school City fan myself but I'll try. When I started going it was 1968 and we had just won the league. As a kid I had just got interested in football through mates, my dad had no interest in it so I never had any peer pressure or was raised with a love of it. For a couple of seasons we won trophies and I thought that it would always be like that but of course it wasn't. I guess I never had enough success to be spoilt but I started from a winning perspective.
Losing or dropping points always hurt even when we were shit. As a fan base back then we ranted and moaned just as much but it was at the game, on the bus back home and at school/work until the next game. There was no social media back then so the real outpouring of anger would be straight after the game as that was the only time you encountered an opposition fan. People would mob up to attack the enemy as they were viewed and this was in quite large numbers. If we had lost or it was against the hated rags, scousers or cockneys more joined in. Plenty also just went straight home but I did see a few heated arguments and the odd punch up even amongst the less aggressive older supporters. This was a normal match going experience.
As the years progressed and we became really shit we became numb to losing and disappointment it happened so often, in fact we expected it. If there was a glimmer of hope on the horizon we always knew it would end in heartache and it often did. So poor did we become that our steadfast support in large numbers as our closest rivals won trophy after trophy became a badge of honour we wore with pride. It drew admiration from opposition fans and the media alike, how times have changed!
So in summary being spoilt by success isn't the reason for any anger or the odd fisticuffs after a game it has always happened as long as I can remember. It is just more visible now due to social media and platforms like this.