Definately super prevalent around this side of the world - And more so in the park. I think this is due to a younger (these are generalisations.) Crowd in the park than the backcountry and generally this crowd is more concerned with what they look like while snowboarding. In a way I think it is part of kinda fitting in with that scene and not getting ragged on for wearing some bogus shit.
Most of these style evolved from skate styles. Really baggy clothes were popular on skateboards before snowboards and same with super tight stuff. I think also that a good percentage of these skaters would board so they kinda cross that style over into there snow sliding.
I also think that this is a type of expression. Yeah maybe people don't wear the wildest s*hit but for most neon clothes are what they usually wear. Personally I spend a bit of time on sorting my riding outfits because personally if im comfortable and feel good about what I'm riding in then this shows through in my boarding - It looks and feels much smoother and I find it easier to progress.