Its all population control. Instead of picking a server that says FULL, they're trying to motivate you to go for a server that has more room. To spread people around.

Ow and please, dont act like its the first time you ever see a queu. Every new expansion in WoW leads to massive queu's, and you know it. And you also know that it doesnt last and those queu's work themselves out after a short while. Its nothing new or uncommon. But if it bothers you that much, feel free to play something else. I dont think anyone here would mind it if there is 1 less person in the queu.