You do have a point, but they could:
* do much fewer batches of consolidation if they want to // no need to do all in one day
* do partial consolidations together with the actual user withdrawals (that would be imho a smarter implementation).
This is a good question and I will come with two thoughts (although one of them may need its own different topic) :
* many traders (ie not actual newbies) could think "if the mempool is this congested, why would I withdraw? I will have to pay a lot to send back when I want to sell" // maybe this is one of CZ targets?
* what if, while we were cheering this year for how much bitcoin has left the exchanges in 2022, this was more due stealing/working on fractional reserve than user withdrawals? (I know, this may be a bit paranoid though).