I don't get it

Whether I live here 10 years or 100, I shall never understand how or why precipitation paralyzes this city. Water, in any of it's forms, falls from the sky and the general population can be heard crying "Retreat! Retreat!". I've thought about it over the years and I simply cannot come up with a reason. People have told me it's the hills. This argument may work for the ice, but has no real bearing on the rain portion. Sure, it's slightly more slick, but the breaks still work - i know this full well because when i travel the interstate in this virtual natural disaster, i'm on and off the break the entire way. What is it about rain that makes the same drivers who usually barrel down the road with no regard to speed limits now unwilling to travel more than 35mph? While i understand caution, i do, I just don't get why the highway turns into a parking lot at the sight of a raindrop.
Another thing I don't get related to rain - it has been my understanding through life that one generally avoids mowing the lawn in the rain. At work it seems they ONLY mow in the rain. Is there something i'm missing here?