I'm by no means saying that they have no further role in the company, and you are absolutely correct that these companies need to continue to innovate. This is why I mentioned transitioning control to a better candidate, because the role of the CEO changes as the company matures.
Smart founders should find a way to continue to play into their strengths instead of clinging to the highest title, otherwise they will always need to be removed.
Its simple greed and disdain for their users that they somehow believe if they begin to charge for something that used to be free the use base will simply eat it and be happy.