I don’t know about the popular choppers that are being built today (Jesse James, “American Chopper”, etc) but the Hell’s Angels originally rode choppers because they were uncomfortable. I guess it was to prove you were “tough” by their standards.
They had small gas tanks (not really sure why on this one…), no suspension (to make it a rough ride) and those big “ape-hanger” handlebars to wear your arms out.
I imagine they’re probably just for looks these days.