I get the sense that the financial motivations - such as they are - may only be part of it; perhaps only a very small part of it.

I’d bet a lot of people do it for the status, because they want to be able to describe themselves as investors.

Whether or not that makes them chumps to people who actually do make real money as investors doesn’t matter so much because they aren’t the target audience for the status message.

Less cynically, there’s also a motivation, at least amongst some, to help people building startups.