Vert is scary to skate properly. So are big handrails. I'd argue though, Vert is more controlled and predictable. I seriously think the risks are higher on the terrain Nyjah skates. So if helmets are acceptable on vert there is no logical reason they shouldn't be on street.
In saying that I also have the same irrational internal bias against helmets and know I would not enjoy street footage as much with a helmet-wearing skateboarder while I would gladly watch Frazier or Schaff all day on an 11' foot wooden halfpipe. It's silly and there is no real logic beyond aesthetics, behind it.
I think it's just a matter of being conditioned. First time I saw kids on bicycles (or snowboards) with helmets I was like, "Whoa." Now it's like "Whoa" when I see them
without helmets. We are conditioned to see vert skaters with gear, so it seems normal. Likewise with see street skaters w/o gear. I mean it was way more normal too see mini ramp skaters with pads back in the day, and no one really gave it a second thought.
But, someone already said it, the (street) game has changed, and things have not caught up. Look at Tommy G. street skating in Future Primitive vs. Nyjah. The risk level isn't even in the same ball park.
As to "vert being more controlled and predictable," I think there is some merit in that. Hawk recently said the reason he thinks he can still skate, at all, because he skates vert and can knee slide (e.g. pads). You can't knee slide down stairs the same way you can knee slide down a vert ramp...which is not to say that vert isn't terrifying (it absolutely is), but rather there are different types of risk factors....and vert might have more a long-game aspect to it than street hammers do. I believe that.
I think helmets are cool, and "tough-guy" egos are lame. More of heavy hitters should rock them, IMHO. But to each their own.