They don't look like hog to me 
From the acronym HOG = Harley Owners Group.
Used to be you'd only call a Harley a "hog", now any motorbike gets that appellation. Especially big bikes, which are usually over 1000cc, so like 1100cc or 1200cc road or touring bikes since they're pretty huge.
I hate that I'm infected by America's mind viruses.
EDIT: Looking this up further, I found this tidbit:
The Harley-Davidson team's mascot was a small pig, which they would take around the track with them on victory laps. Weishaar was particularly fond of it, and many photographs exist of him and the pig. It is because of this mascot that Harley-Davidson motorcycles are called "hogs."
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy:
lumberjacks and wildland firefighters also call big trees hogs. i spent a whole summer laughing about that when i found out
I think its cuz when you rev their motors it kinda sounds like a pig squealing.
Whenever I see a guy on a motorbike (UK) I say some variation of "damn that's a fat fuckin hog"
