It started going pear-shaped at the height of their success. The GPC turned them into the most hated club since Leeds in the 70's because of his 'win at any price' ethos: cheat, feign injury, dive for penalties, intimidate officials, use a sycophantic media to spread venomous bile about opposition clubs and players. Outspend every other club, ultimately buying every trophy in that fucking cesspit they call home, and do your level best (with the assistance of David Gill) to stop any other clubs from doing the same.
It was always going to be downhill for them the moment Kim-Jong Pisscan retired (nobody stays top of the pile indefinitely), and because of the way the club and the plastic fans (under the domination of the bully) behaved towards everyone else, specifically us, they burned every fucking bridge there is to burn and are now finding out who their true friends are...ie, no fucker.
If that club had acted with a little more decency and respect they would -albeit begrudgingly- be respected for their achievements. But as it is, most football fans are enjoying them crash and burn. I know I bloody well am.