most startups fail. the likelyhood that the earned equity will be enough to kickstart my own project years later is to small to be worth the risk.
if i join someone for equity, then it has to be a project that i am actually interested in enough that i'd start it on my own if i had the opportunity.
so it's not my project vs your project but it is my interests vs your interests. if our interests align, i'll join you, even for equity only.
however at the end of the day i still have to put food on the table, so if you are looking for 100% commitment, i simply can't afford that.
i was part of a startup based on that premise. it failed because noone could put in enough time, and the founder rejected the idea to finance ourselves with consulting work believing that if we did that we'd never get to work on the startup because we'd be busy building up a consulting firm.
i don't believe that's true, because somehow i manage to make a living from consulting and still have time to work on my project.
it's all about priorities.