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Also - Why are they not going to be co-founders if the risk profile is exactly the same?

Cofounders get much higher expectations so they get more equity. Basically the same thing, just less equity.

Yes and I'm curious what pool of workers don't need to get paid but would be open to gambling their time on the riskiest of bets

What else what they put their time on? side projects that for sure don't make any money?

Their own startups. Your startup, from their perspective, is just your side project.