Keeping the "Public" in Seattle Public Schools

Why do we have so many philanthropists and education non-profits in Seattle who insist that they take over our schools instead of systematically and comprehensively improving all schools? I have to question the motives. They should open their own schools if they need clean Petri dishes for their programs. If these folks want to be a part of the success of public schools, they need to be supporters, not highjackers.