Why do certain cryptos all drop simultaneously at a certain time of the day...?

Fairly new to crypto and just getting my bearings with this fascinating landscape. Trying to recognise the patterns over the dayd and nights and I've noticed more than a few times that trades all seem to drop simultaneously at the same time during the day and night. It happened just now at 5pm across the board and I've seen it at midnight a lot for various coins.

What is the reason for this? Is it a deliberate sell-off by holders or a result of general activity across the world or maybe something else? Maybe multiple factors at play? Curious to know.

Many thanks!