And maybe it’s not. The big mistake people make is hearing non-profit and think it means there’s a greater amount of morality. It’s the same mistake as assuming everyone who is religious is therefore more moral (worth pointing out that religions are nonprofits as well).
Most hospitals are nonprofits, yet they still make substantial profits and overcharge customers. People are still people, and still have motives; they don't suddenly become more moral when they join a non-prof board. In many ways, removing a motive that has the most direct connection to quantifiable results (profit) can actually make things worse. Anyone who has seen how nonprofits work know how dysfunctional they can be.
I've only really been close to one (the owner of the small company i worked at started one), and in the past I did some consulting work for anther, but that describes what I saw in both situations fairly aptly. There seems to be a massive amount of power and ego wrapped up in the creation and running these things from my limited experience. If you were invited to a board, that's one thing, but it takes a lot of time and effort to start up a non-profit, and that's time and effort that could be spent towards some other existing non-profit usually, so I think it's relevant to consider why someone would opt for the much more complicated and harder route than just donating time and money to something else that helps in roughly the same way.