[PapaBear3625]

The dirt bike/ATV gangs have become common in urban areas even though there aren’t any trails or open areas for them to ride on.

Because they're cheap ($1,000 to $3,000 new), and you can get away with not having a drivers license, insurance, registration, etc. That can make them popular with ferals.

[Iceclimber58]

Are they chinese bikes?
I have not messed with dirt bikes since the mid eighties, but a new Honda cr250 was about 2500.00 in 1986.