It is the same situation around here during daylight hours. Sailboats are almost never stopped.(I have never seen one stopped, but I hate to say never)

Story number one is that none of the law enforcement entities will stop a sailboat because they are such a hassle to deal with. Sails up, boom, rigging, hard to maneuver, can't just stop, hard to tie up to, etc.

Story number two is that for the most part, sailboat owners are more experienced boaters and tend not to do stupid stuff. Whereas powerboat owners tend to pretty much all do stupid stuff and only require money to buy the boats and keep them in fuel, no skill required.

I think that a relatively unskilled, unprepared powerboat driver can get into trouble quicker with more dramatic results.

After dark, the border patrol seems to be equal opportunity. They will pull over most anything.