[ronack]

"not already a millionaire"

When your company is where Snapchat was at the time there's a good chance you've already taken millions off the table as part of a round. Even if not, when your company has achieved that level of growth, you can feel fairly confident that you will walk away fairly wealthy in the end, and it's more interesting to continue running your own company than it is to be rolled into someone else's.

[erikb]

The first reason makes sense to me. Maybe they are already, because there are other ways to take money (or money like values) out of your company besides selling it.