Because they are only giving it away for free for a limited time.... it's a promotion for the software... they aren't actually making the software freely available in general.
The alternative would require that they prepare a special version of the software that doesn't come with the DRM solely for the promotional period... which because of how short it is, it probably wouldn't be worthwhile.
Not that I agree with bundling this software with their game... I remember having it on my system once with some EA software and it caused me a lot of grief (affected my DVD drive in unexpected ways). I haven't installed anything from EA on my computers since, and I doubt I ever will.