Why would they use it? Purely due to Sega?
Honestly, I don't know. They should be using every available opportunity to hype and sell the game - if you market anything well, it will sell well, even if its complete crap. Im not saying CoH2 is crap, but I'm saying, if they did better marketing then they'd sell more units, and the NDA directly inhibits this. It could be down to Sega, but I think this kind of thing has been in the companies DNA before the sega acquisition and probably comes from internal management. I can see why they would want to be a little secretive, showing something in Alpha or even Beta then getting uproar from the community when it gets removed creates another nightmare in itself. But thats down to them not sticking to their guns and being indecisive really.
In my eyes, do a private "public" beta when you have decided what units, abilities are going to be in the patch, then use the beta to test the balance etc, only remove something if it causes stability issues or was a serious mistake. This would tackle the one step forward, two steps back problem we face at the moment.
Personally, I think a lot of the problem related to balance is the fact that there isn't enough unit choice with the armies, there should be a lot more core units to entice different play styles. There shouldn't be only one counter to unit X.