Well, legal stuff and also you just don't badmouth people you worked with until recently. It's simply not nice, and we are still friends with some of the Inc employees.

For more info I recommend the Q&A from Frank and Jos today: https://youtube.com/watch?v=iMfokaX2r8g – we try to be as honest as we can.

Disclaimer/source: I'm one of the »poached developers«, or rather the designer. ;)