What happens when your startup is acquired?
dondodge.typepad.com
Success depends on founders and acquirers sharing vision and control
dondodge.typepad.com
I think that it often works in reverse: the acquisition fails, causing the founders to leave too soon. I don't doubt that some founders see the $$$ and can't wait to leave, but there are lots of founders who genuinely want to thrive at the new company. Sometimes the acquired startup doesn't get the attention or resources it needs to successfully integrate into the new company, or maybe it gets put on a back burner. That may cause a founder to want to leave.
It’s no real secret that Google wasn’t supporting dodgeball the way we expected. The whole experience was incredibly frustrating for us – especially as we couldn’t convince them that dodgeball was worth engineering resources, leaving us to watch as other startups got to innovate in the mobile + social space. And while it was a tough decision (and really disappointing) to walk away from dodgeball, I’m actually looking forward to getting to work on other projects again.
(http://gigaom.com/2007/04/15/dodgeball-founder-quits-google/)
At a brief glance, it appears that when you get a lot of autonomy and resources (YouTube and Android), you want to stay. When you feel like Google is ignoring you, you want to leave. That's the way it looks to me.