People probably want to be the first to try something that, if it worked, would change humanity as we know it. Or even just contribute to the progress in their own way. Money is hardly the only motivation for many things, nothing stopping them from owning Tesla stock if they really believed their involvement was going to make billions though.
How would a self driving car "change humanity as we know it"?
Sure it might make travel by car suck less but not in any significant way that would change humanity in any meaningful way. At least not outside of a very narrow bubble we might be a part of.
