Can be due to forgetting. Many start the clock as a reminder, or set one up in the box 20 mins after just in case you forget.
the Cabin Crew are pretty good at reminding you. If we encounter occasional moderate in a forecast area of Mod or Severe, I would say we are duty bound to keep the signs on until we see the ambient temperature changes stop.
Same with flying in the vicinity or downwind of Thunderstorms/Cb. No one wants passengers ricochetting off of the roof. CAA will ask questions and if you ain’t on the right side of safe if someone gets seriously injured, and it can be proven you are incompetent, it could cost a licence.
There are other circumstances, for example, violent passenger or medical issue et al, where it is prudent to keep people seated.