Really? You would make that call? Well I guess were all lucky that EA/DICE are able to weigh pros and cons better than you panda
Obviously they knew that if they had a closed alpha some people would leak footage, but they at least recognized that testing and building a great game is more important than keeping everything under wraps till launch. To bail out at this point would make them seem very foolish for assuming people would honour the NDA in the first place (which I'm sure they did not lol)
If the game is good people will buy it regardless of whether or not alpha footage was leaked so I don't really see the disadvantage, where as the disadvantage of releasing a sub par game (especially considering how much trash talking they've done about COD) is they don't sell as many copies and they lose their fan base.