I don't think you understand. If you join my startup team and spend one weekend working on it and then disappear for a year while everyone else keeps working then you didn't build even 1/2% of the effort. Anyone that thinks a weekend of work can generate 10M of value is delusional. It's better to keep them filtered out of the process from the start.

And just to clarify - if everyone on your team signed away their rights then you would still be free to take your code and do whatever you want with it. You could build the business on your own if you didn't like any of the other teammates.