It could be the exchanges withdraw the coins to their own cold storages, I still believe most people hold their coins in exchanges.
I'm also skeptical about this onchain data. I don't know if this is a reliable source of information so we can follow the market's money flow or if this is what the market makers want us to see and believe. People who follow the school of technical analysis trust these data sources very much and they consider them as a measure to determine market trends. But some never trust on-chain data.
Look, this is nothing different with those self pro claimed professional trader is promising to get rich by trading, in his group he will share
his fake signal and he wrote "trading is high risk of losing money, DWYOR, myself (self pro claimed professional trader) won't liable with any losses".
They create the statistics, but they didn't completely trust with their own stats lol.
Disclaimer: Exchange balances presented are derived from Glassnode's comprehensive database of address labels, which are amassed through both officially published exchange information and proprietary clustering algorithms. While we strive to ensure the utmost accuracy in representing exchange balances, it is important to note that these figures might not always encapsulate the entirety of an exchange's reserves, particularly when exchanges refrain from disclosing their official addresses. We urge users to exercise caution and discretion when utilizing these metrics. Glassnode shall not be held responsible for any discrepancies or potential inaccuracies.