Most people are also easily flattered and everybody is naturally opinionated. It's hard to keep your ego in check.

For example, you see respectable scientists and artists write a popular book, then the next one (because their publisher nags them), then a third one that is borderline unprofessional (no time, publisher send ghostwriter), and so on. Maybe some of them realize that a best seller can yield a lot of money and in no time time they appear in talk shows talking about topics they couldn't possibly know anything about (alien invasions, politics, the future of mankind). Finally, they appear to be nuts and everybody is angry about how "fake" they are and speculates about their mental problems.

If I would get book proposals and interview requests every day, I'd probably end up the same way.