Here's a good reason: we're not interested in broadcasting those figures to the world. That kind of information is usually kept internal, and there are good reasons for that.
I just think that more communication and more transparency is a good thing. I am not saying that we DESERVE to know the size of the waves...like I said I just can't think of a good reason why bioware would not give us this simple piece of information.
Here's another reason: even if I gave you exact numbers, it actually wouldn't help you understand when you'll get in. (Which is why the charts circulating showing 'pre-order numbers' aren't actually helpful. Those numbers are based in the most part on guesswork.)
Here's a third reason: it'll cause more problems than it solves, right now.
I'll have an update later on today's invites.