Same reason they drive faster in Fog, Higher state of awareness in the conditions, tunnel vision and lack of experience. Then throw in that Californians drive older cars than the rest of the country, defer maintenance on vehicles and buy summer tires rather than all-season tires due to cost and in spite of adverse weather conditions. Californians tend to look like amateurs, Case in point is the " people behaving badly" videos done by KRON in San Francisco. Drivers spinning, sliding and crashing in light rain. CHP pointing out bald tires and drivers acting like they just learned to drive. And I am referring to out friends in the cities, NOT the rural and mountain drivers. Anyone who has been on Ice never forgets the feeling, Same with snow.

It's everywhere. Not everybody does it; in fact, only a few do. They are gonzos who drive too fast and loose anyway but really enjoy showing off their stupidity in the rain.

because the vast majority of people behind the wheel of a vehicle are just drivers, as opposed to those who have the proper training to be operators of motor vehicles, especially those who have had driving courses i.e.the smith system

Adrenaline from seeing a rare form of weather.