Went on a ride today and there was a Vulcan with a car tire. He stayed with us on the curves. Slow turns in the parking lot were the only issue. Not sure what inclement weather has to do with it, cars handle fine in the rain and there should be no difference with a bike.
As for why they ride, if you have to ask....
Big difference between a car and a motorcycle: mc only has two wheels/tires. Huge difference in traction especially in inclement weather. No bike will ever match a car in terms of generating g forces on a skid run.