Non-competes are unenforceable in a lot of places. And even if they weren't, the time scales for a startup to evolve into a serious market mover is longer than

Non-competes are unenforceable in a lot of places. And even if they weren't, the time scales for a startup to evolve into a serious market mover is longer than most non-compete contracts last anyway. A founder of a now-popular startup worked for Google eight years ago, so what? Let's say Google remembers and decides to pursue action. They'd spend another 3-4 years suing a person who has a mountain of plausible deniability to hide behind. And for what? There's no real gain to Google for this.