I think the reason behind it all, a lot of fans were expecting so much like Thriller that he was dedicated to take anything to please fans. The sad thing was as time went on, he was musically going to be ignored and Michael Jackson tried everything that was new to appeal to his fans. I think what happens if you expect so much of Thriller, you would want something to top it off or better yet repeat the formula.
The insane thing was that MJ was hardworking himself. He never gave up on trying. True, his lifestyle was bizarre. There were a lot of WTF moments through his whole life in Neverland Ranch and how he treated his children by wearing masks, but I believe there is another reason to it. Sure, he made mistakes and must be question about sanity, too, but the main blame has to be the entertainment industry.
You must remember the entertainment industry still is pretty like the Mafia, no different from the movie studios or the porn studios. I am pretty sure he was injured on some of his music videos as well as his studio recordings to his popular songs. It was not just Quincy pressuring Michael Jackson, but a slew of promoters trying to get their star to finish this album they have.
I can imagine the scenario:
MJ: I am injured and I need medical assistance.
Promoter: Fuck that! You have to finish this album before the deadline. I made good money off of you for years. Wait..Wait...I have an idea. Dr. Feelgood!
And I believe that's how it works. These promoters don't want a complaint. They shoot him with drugs or whatnot to keep the star to finish an album they were suppose to do. It's a sick industry and it is still going on to this day. Could MJ have said no to all this? I believe he would have, but he was dedicated to his family and to his fans that he never gave in to retirement. I think that could have been another reason for his downfall as well.
You might disagree with me on that, but that's the way I see it.
And some might argue with this, but I believe the Jacksons were a very naive family as far as money talks. Some of the problems stemed from the father and their religious Jevovah's Witness mother. Hell, most of them with the exception of Rebbie and Janet, all stemmed from financial troubles. This was not a very money stable family to begin with. I am pretty sure Michael's money troubles would have happened before or after his fame. But since his death, he is worth more dead than alive.