I don't want to wade into the "is it folk?" quicksand, but I suspect that not many other genres/styles/traditions of music prompt such regular & heated debates about what 'qualifies' for the label & what does not.

This could be because (a) the borders are so porous and easily 'breached', or (b) because it's a musical arena that excites passionate defenders, or...both of those reasons & a whole lot more besides.