They may be fender bigots.
OR
Maybe their butt gets itchy and it seems like a good way to scratch it.
you know, (just ease back and lower).

Tried it once on a bicycle and it burned the devil out of me.

I still think for it to look good it should be a hard tail and about 1 inch/18mm from the tire/tyre.
JUST a little space for swell for when you pass the HD's at full throttle.

Worth