Because some people decide to receive there signature payment on exchange doesn’t mean they are holding the bitcoin there, after withdrawing some might just decide to make use of p2p to convert the amount which they want to there local currency, and just send the rest to their non custodial wallet and hold. I can still remember so well when the gas fee was kind of high, and people were finding it difficult to make transactions, even campaign manager were finding it difficult to make payment then, I guess that was when people decide to make use of exchange to make things easy for them, but some people didn’t request for change of wallet when the gas fee went back to normal, and they keep on receiving there payment on exchange, but that doesn’t mean they are holding on exchange.