Free option? Vanity? You get to know the books, the team, etc. And if before you ("VC") haven't been figured out the startup gets traction, you can find money to get in (maybe).
I think you hit it with the free option. They are syndicating their investment as soon as they have some sort of agreement and they probably have some contigencies that allow them to get out for any reason in the event they can't find investors.