The part missing from your hypothetical scenario is that founders have egos and many would rather keep ownership of their company and don't want to work for someone else. (I made previous comment about this.[0])
Yahoo made offers to buy Google and Facebook but we obviously know that Larry Page and Mark Zuckerberg did not become employees of Yahoo reporting to their boss Jerry Yang. They said "no sale".
In Facebook's case of being the buyer, Kevin Systrom of Instragram said "yes" to Zuckerberg but Ev Williams of Twitter said "no".[1]
If you're a founder of a successful startup and Autodesk/Facebook/Google come calling with an offer of (m|b)illions to buy your company, you can listen to them but you don't have to sell.
[0] https://news.ycombinator.com/item?id=21419098
[1] https://techcrunch.com/2013/11/04/the-three-reasons-twitter-...