I really wouldn’t get it why people would prefer to use exchange addresses in receiving payments and not have to send it there themselves from a custodian alternative.
They either don't know about custodial wallet and non-custodial wallet, importance of private keys or they knew about these things but don't mind to follow recommended practice.
Perhaps it could be the fees but, I find that to be a very lame or dumb excuse. It doesn’t cost much on fees these days, it’s always ranged between 1-10sat/vByte and you would have your transactions processed really fast.
Convenience and saving in transaction fee are two main reasons. By using an account on a centralized exchange, its account's Bitcoin address for receiving signature campaign payment, they will not have to broadcast any on chain transaction and don't have to pay extra on chain transaction fee.
They have such a reason but if they know about risk of centralized exchanges, they would have different practice.
Reminder: do not keep your money in online accounts.