Players have a choice right now. And what are they doing? They're re-rolling alts on "The Fatman". What are they going to do if they could choose any server they wanted for a free transfer? They'll move all their abandoned characters to "The Fatman".
This would be disaster. It's pretty obvious why they have restrictions right now.
You're making the assumption (azz out of u and me) that everyone would got to Fatman. I sure as heck wouldn't. I'd like an active server, but not a full/packed server.
Also, you're assuming that they'd keep letting more and more people pile into a full server. If the server is "full" they wouldn't allow any more transfers to that server until it's no longer full. Problem solved.