Driving in the rain

Around here (SF Bay area), why is it that so many people see two raindrops and slow down by 15-20mph? C'mon, you still have miles of visibility and it's not much more than a drizzle, anyway. Half of us are transplants from places where it really rains, this stuff from the sky should not be a surprise, especially since on rare occasions it does rain rather heavily here. I guess it's the short attention span of the general public. (Hint- if you can't see through the windshield, got off highway, clean said windshield, and replace wiper blades. Better? Or maybe, just get off the highway all together.)