I have this same problem. The guests act like they want to ride and go to the queue, but turn away again before actually getting into line. I tried looking at their thoughts, but they don't have any thoughts about the ride. It's a safari car ride, and it has had ZERO riders because they can't get on.
I use the queue pathing for the entrance, and regular pathing for the exit. When it wouldn't work, I deleted the pathing and tried laying it down again, thinking there might just be a placement issue, but it didn't work. I picked up the entire ride and placed it down again for the same reason ... didn't work. I tried placing a lot of flowers and stuff to a make it pretty, but that doesn't seem to be the issue.
The game won't allow me to just delete the entrances and exits and place those down again separately.
The cars will run by themselves (empty) around the track, so the track itself works fine.
Any ideas?