Ive only seen fat, older people on those 3 wheeled ones fwiw
The ones I have seen are about 50% split btwn fat/old and normal not old. I imagine it has a lot to do with where you are seeing them.
Also, a large majority of the street bikes I see are in the same fat/old crowd.

I think before anyone buys a bike they should consider what they look like from the next car over's perspective. I mean, a bike could be for men what pants that make a woman's ass look big are to women.