Another interesting observation by one of the users is that the pools started doing this in November to January [3] so it's likely either miners selling bitcoins to prep their post-halving warchests, feeding the ETFs or both.
Bitcoin miners had to sell considerable bitcoins before the halving actually are not big miners. They did not do anything wrong because with their financial budget, not deep enough, they must to balance it to keep their mining operations continue after the halving.
In contrast, if a Bitcoin mining farm is big and has good financial budget for their mining operation, they will keep their bitcoins and wait for higher price after the halving. Selling bitcoins like this will not help them to maximize their mining business but nothing is right or wrong, it depends on their business model and finance they have.
After the Bitcoin halving, if price won't rise quickly, small Bitcoin mining farms will have to stop their mining because they will get negative net mining income. The rich will get richer and big Bitcoin mining farms will get richer with halving effects.