If for example Viktor Winer did DCA with a small amount of money, I also agree that the right action is to store his bitcoins on the exchange first so that the bitcoins increase and after they have collected more, then the bitcoins are sent to a personal wallet.
The purpose of investors storing their bitcoin on a centralized exchange during their accumulation process is not for the bitcoin to increase in value in the centralized exchange but for them to actually accumulate enough bitcoin so that they can withdraw it at once to their personal non-custodial wallet and also pay for the centralized exchange withdrawal fees at once too, rather than withdrawing their bitcoin on several occasions when they have not even accumulate bitcoin that is worth $500-$1000 and end up paying for the centralized exchange withdrawal fees anytime they withdraw their small bitcoin to their personal non-custodial wallet, which will make them waste a lot of money paying for centralized exchange withdrawal fees.
I still sees it as a terrible decision leaving your Bitcoin in a centralized exchange regardless of what so ever because if anything happens to that exchange in question like hacking or internal theft your Bitcoin is good as gone, but in this case where you are using it to buy Bitcoin through the DCA accumulating strategy, and the fraction of the Bitcoin is too small to be moving out anytime you make a purchase, in my own opinion, I would rather wait and be withdrawing it to my self custodian wallet on my second purchase, and it must be weekly, like every two weeks, keeping it for a month is too risky, so I will be moving my two weeks purchase to my self custodian wallet every two weeks, anything more than that is too risky , it's better for me to pay the higher transaction fee and my Bitcoin is safe, than to be greedy and be risking my Bitcoin by leaving it in an exchange for longer duration.
Whatever reason they have they should never leave their Bitcoin on centralized exchanged since they provably putting their money at risk of hacking. For many times we already experience those big exchange hacking so hopefully this is already enough basis for people to believe that its bad idea to leave some amount on their exchange accounts.
Withdrawing it to their personal wallets didn't eat to much of their time so people should not be lazy for doing this since this is for their own good. Some may think its a waste of withdrawal fees for frequently doing it, but if we talk about safety for sure those amounts we pay for fees is nothing especially we are sure that our funds is safe and away for any possible treats. I'd also prefer to pay fees for my own convenience rather than trying to risk my accumulated funds on risky platforms.