Because it is good and people want to do selfish things.

The end result is fragmented projects, worse developers and less activity. Congratulations. You got your social point across to the detriment of everyone.

Power tripping. Ever wonder why projects become "foundations" with heavy emphasis on non technical bureaucratic bloat, committees, forums, "community managers" with way too much power and so on?

The main reason to become a foundation is to have some legal entity to deal with money. Some times projects get grants or donations or google summer of code mentor payments, and that can either go into a random account of whoever happened to be in contact with the donor, or it can be properly managed by a foundation with agreed-upon guidelines on where to store money and what it can be used on.