i'm guessing that some of it has to do with the fact that some of these guys are messengers, commuters, or folks who just enjoy riding a larger bike around. it makes sense in a utilitarian respect to at least explore merging a flatland bmx experience with your daily grind if you're riding a larger bike around already anyway--and hanging out with others who do the same.
i find it interesting in its practicality in that respect--that it's just this thing that was kind of borne of convenience.
i also see adoption and mutation of the bike ballet stuff on the not so distant horizon. adapting that sort of grace with more aggression and, well... recklessness, is something i look forward to seeing evolve.