Why does Yamaha waverunner stick in reverse?

There is a cable that connects the reverse handle to the reverse flap down by the jet nozzle. If that cable has any damages in it or to it..... it will stick or feel harder to engage/disengage. If this is the case then you need to replace the cable. There may be a slim chance that there could be something jamming the connecting device by the nozzle. Consult your manual, look at cables inspection.