WAV, i can't decide whether you're being deliberately obtuse. The point is that Music Hall was considered vulgar and populist by most of the collectors. This will be for myriad reasons that are no longer particularly relevant, because we can't really see music hall in context as we're viewing it from a distance of 100 years; the point is, but it was the popular music of its time. Performers would have deviated substantially from what was considered traditional music, and also from what was considered the "correct" way to sing traditional music. Just like pop music deviates from your ideas of what is acceptable. But many of the "source" singers still loved music hall, and sang it.

The whole point is that traditional culture should not be viewed in opposition to popular culture, but rather as something that exists alongside it. Neither is more valid than the other.

Blimey, it's not bleedin' rocket science, is it?