Short-term dumps used to be near the previous halvings. Trying to take advantage of erring on the side of caution is common for groups of people. Halving is a big event that, if something goes wrong, can cause trouble. It's like changing your car's engine and taking it for the first test ride. Some people will bet on this ride ending in a system failure, even if they know that the swap has been made in a professional way. There's always that doubt about new things if they're going to work.