They can, though? They just have to pay, and if it was an issue of any significance, that would only be a one-time fee because everybody would do it and be on the populated (“dominating”) server. They aren’t going to pay again to transfer it the sever being dominated, and other servers aren’t exactly going to catch up, because the moment a new player joins and plays a brief amount of time, they’ll realize the same thing and pay the one-time fee to transfer and the cycle will repeat itself.
Locking someone to a server simply because they clicked on it isn’t going to solve that problem by incorporating a fee of what, $30 or $40?
That also doesn’t mention that, at least when comparing it to my situation, they would have to completely start from scratch (losing their characters, items, progression, etc.).