Because:
- this is data from glassnode, a company which I will never forget for making this stupid shit up
- there is really no way tracking conveniently those coins, they might be going outside of Coinbase's cold wallet but nobody knows who's those wallets are until mode data is revealed
- companies tracking those movements have a lot of time made a fool of themselves by advertising as mysterious transfers that were simply cold wallets funds migrating to another new cold wallet.
Going away from blaming the poor data
- coins that sit on exchange and on exchange wallets are not coins that definitely must be sold
- coins that leave the exchange are not definitely coins moving to hardware wallets, they might be coins moving to bisq to be sold
- coins that leave that exchange might be coins who have been sold by the owner to somebody else, so thus the drop
- 1 million coins that are used to convert back and forth BTC<>USDT will not have the same effect as a dump of 1500BTC which right now would crash even Binance to under 40k.
- and most important, nobody knows how the amount of $ on exchange is fluctuating.