Most people's "depression" is caused by poverty—having 100 million in bank savings would probably cure it.

People who are wealthy yet still depressed and suffering mostly earned their money through disreputable means. They had to struggle with all sorts of shady characters, some lost their dignity in the process, some took the risk of breaking the law and going to prison, and some risked their lives. It's normal to be depressed with money earned that way.

People who have accumulated enormous wealth through making legitimate contributions to others and society won't be depressed.