Re: The reason is fairly simple
@Boris the Cockroach
I challenge you to find a single example that's actually followed that route - especially the 'moving the factory to China' and 'suing' bits.
If the company was ever to be a success the wine glass would have been made in China in the first place. You're going to sell your business for a lot more if it has solid patents and non-compete clauses to protect it from competition. It's in your interests not to go and set up a competitor (or, more to the point, not be able to do that) the minute you leave.
The "problem" (if there is one) is one that you do mention - investors want to cash out, not build something permanent. Sometimes the founders want to bale out as. All of this is neatly illustrated by one Lastminute.com.
But is this really a problem? That happens everywhere. All the big American internet businesses are constantly acquiring start ups, so someone must be selling them. The UK tech sector is doing fine. There are few to no equivalents to Google and Facebook anywhere else in the world without a Great Firewall. I sense collective 'wisdom' and confirmation bias at work here.