I think it's because he seems like that God,-like man who is going to lead you to the promised land! He's like a TV preacher, he's got that charisma and you went to follow him! And give him a billion dollars.
Oh they went to __ school, they must be good. Oh they worked at __ co, they must be good. Oh they worked under __ [team/manager], they must be good. Oh they launched a [fund/startup] before, they must be good.
Once you get the foot in the door once, it's easier to get your foot in the next 10 doors.
The real reason is that dropping him after the first big losses would make it clear that you f'd up by backing him in the first place.
> because he has the resemblance of the kind of messianic white guy that is able to take a product and sell it