According to an analysis from the Federal Highway Administration, 46% of all car accidents over the past 10 years were due to rain and 73% were caused by wet pavement. This increase could be attributed to the increase obstruction of ones vision when driving in the rain. (https://ops.fhwa.dot.gov/weather/q1_roadimpact.htm)
Students tend to walk out into crosswalks quickly when trying to get to class, causing cars to stop abruptly. This can result in skidding or hydroplaning, which puts pedestrians at risk. Students who walk along side main roads on their way to class are put in serious danger. All it takes is a single accident to permanently ruin someones life.
People also tend to rush in the rain to avoid getting wet. With this number of students partaking in rain-running, there is the serious potential that someone could be injured as a result of wet surfaces. Students are then left feeling as though they are between a rock and a hard place; either they can go slowly, get wet, and be potentially late for class, or they can attempt to run and risk injury.
In thunderstorms, the National Weather Service advises that you take cover immediately. When thunder is heard, lightening strikes usually within 10 miles of rain.
Not only do the students want to stay dry, so do their professors. It's not worth a professors time and effort to leave their homes, drive to campus, park their car and walk to the lecture hall to show up to a room full of chirping crickets.