A lot of the startups that I see that try this are doing it because they really believe that they're bringing the value in this relationship - that they're going to be so successful, there's so much money here, they have SUCH a good concept, that the applicant should be
grateful to get in on the ground floor.
Of course, 90%+ of the time they're totally wrong about everything about what they're bringing to the table, and in the other times, they'll often conveniently change things around to benefit them, like, "Well, you know, I know we said 4% of the company once we raised series A, but honestly, your contributions have not been what we expected, and so you really only are entitled to 1%"
To quote "The Spanish Prisoner":
Jimmy Dell: I think you'll find that if what you've done for them is as valuable as you say it is, if they are indebted to you morally but not legally, my experience is they will give you nothing, and they will begin to act cruelly toward you.
Joe Ross: Why?
Jimmy Dell: To suppress their guilt.