Why does nobody talk about how a sudden downpour can turn a perfectly graded trench into a mudslide nightmare?

Had to evacuate the site yesterday when our trench walls started collapsing from the rain, and now I'm looking for better drainage strategies before the next storm hits.

I mean, idk how I managed to binge a thriller series with the brightness all the way down because I thought my screen was broken. Missed every crucial clue.