Because:
1. If you work on tourist visa, your defintely need to exceed the allowed period of staying, let's say a month, and you are destined to become illegal _resident_; but when you come as startup founder, you will be _legal_ resident, inot matter if you __work __ illegaly.
2. Now you came as a startup, what you can do - instead of making a new unique product you just go and work with a software giant, doing let's say testing. Who is gonna watch what you are actually doing?