Perversely I really don't mind riding in the rain and if you take away the getting soaked element, find it a very rewarding experience. Riding when its wet has taught me more about bike, throttle and brake control than any dry day could possibly. Its taught me not to fight the bike, trust in whats underneath me, but most interestingly, its taught me a great deal about reservation.
With upwards of 150bhp on tap, with no electronic aid, going straight to the rear wheel, being smooth is the only option. Big sharp inputs would leave me in the nearest hedge and that would have a good chance of ruining my day.
Yes there are many reasons not to want to ride in the wet. Getting soaked and getting the bike filthy are two very strong reasons, but for me at least, the pros far outweigh the cons.