That's because they're founders and CEO's. If you're hiring me, by definition I'm not the founder (but if I have lots of equity and am treated as an equal partner maybe we'll split the difference on that one). Are you hiring me to be CEO, then? If not, find a better example to compare me against.
Someone who tries a corporate job for four months, realizes that he isn't getting good projects, and leaves, is (a) doing what he should do, since he's undervalued in his current role, and (b) not really hurting anyone.