How come that even Jack Ma, the founder of Alibaba and is one of the richest men on the planet, said that his happiest days were for him as a poor teacher, where he earned 91 RMB a month.

Maybe that was less stressful for him. Many people cannot (unable to) (and/or do not even want to) handle fame (and other circumstances). Many famous actors/actresses, singers and other people "escape" to use alcohol or even drugs, and ruin their own lives.

Not to mention the fact that owning/managing a huge, worldwide company, like Alibaba comes with a huge responsibility and stress. Even Elon Musk said that he do not want to be the CEO of Tesla. He just have to. Or at least he said that Tesla would die if he was not CEO.