I think the rot set in after there they got the title a few years back. Almost as if they were saying to themselves 'We're back. The good old days are returning. We only have to turn up and the game is ours.' Relying on past glories to carry this mythical reputation of being the best of the best.
The more they tell themselves they are the bestest club in the whole world the more they believe it. They come across as so arrogant they believe it is an affront to win a game against them, that all clubs should just surrender to them the moment the match kicks off. And judging by the posts on RAWK I would suggest that both Bingo and the sycophantic media in this country planted these delusions into their collective heads, and have continued to cultivate these seedlings since. Knowing they will grow to be the inbred, neurotic, unhinged proles they have become.