Well for one, they are the most repp'd brands
I can't speak for RG cause I don't spend as much time there but here there is a genuine love for Vintage here at RWG
Vintage Rollies are by far the most talked about topic here and the bulk of the community Rollie interest.
There is no denying the history of PAM's and their relation to diving - just read up on it - it is fascinating stuff...Yeager worthy Dems
I happen to like Panerai - the Brand, the Style and the design. They are fun to build, parts are readily available (even Gen parts - just ask Beano ) and there are a lot of options (Ti, PVD, SS polished, Brushed - straps....)
I don't like Bling....some do - it is all personal preference - beauty in the eye of the beholder
I think the HBB is hideous - others covet it