That seems to be based on the 4-year winter cycle or halving cycle. We are already nearing the same cycle closing and which means heavy drop in price of the bitcoin because most of big whale miners around the world will be profiting from the same. If they sell at the current price then definitely it's gonna be worst for them, idk they may loose profitability in the process.
However, I believe that this is just one of the reason for the same but may not be firm one.
There is impossible judgment for the current situation of bitcoin.
i personally have hoards form 2012 prices so im classed as a old whale (but im not selling any time soon)
all the other old whales and miners with coins acquired below $15k value that are selling now. are giving to buyers who are setting their value at the prices they bought at above $17k. giving a new support with higher percentage of holders that have a new acquisition value(buying price) above $17k.
meaning there are less people still with coins able to profitably sell for under $17k than last month thus less people willing to sell below $17k than last month
so my opinion is let them sell. let there be less people able to sell for less. because the long term result is that it builds up support for the 'bottom' to go up