It's like any workplace, ever.
Once moral starts to go, regardless of the reason, it's very difficult to stop, it spreads like a disease. You can temporarily get things back on track by scaring everyone or promising things will get better, that might buy you some time, it doesn't fix the problem and it certainly doesn't work multiple times though.
The only way to reverse course is to locate the "bad" apples and get rid of them or hope they eventually quit on their own (not really possible with contracts though..).
I think this is exactly what has happened, for whatever reason the players became disgruntled. Nonis went in and "scared" the team, they responded but because the underlying problem was never addressed it just festered until you get what you have today. Nonis should have been more active in locating the problem (regardless of it being coaching staff or players) and made the appropriate adjustments.
So at the end of the day, I blame Nonis for failing to properly assess the situation and take appropriate action. He went with the band aid fix rather than the changes required to turn things around long term.
What they get paid is irrelevant, it's the "norm" for them to make so much money. Human nature doesn't magically change because you are getting more money.
More on topic, the fans certainly don't get screwed. You know what you are paying for up front, there is no guarantee of any result. If there was who would care about cheering for a winning team?