There's way more important things to spend their time on. Maybe AMD should make TressFX more attractive to implement first? Oh and they could also help pay the bills during development, and cover a lot of advertising costs with the money they don't have. It is what it is. As far as I understand, nvidia went to great lengths to make their Gameworks tools as painless as possible to implement. I'm sure it was a time saving type of decision, as well as financial.
Admittedly, I do not know all the ins and outs, but if I were a developer, I'd certainly rather partner with nVidia. It's just good business. Shorter development time, nvidia does a lot of advertising for them, etc etc. TressFX seems like a lot more work and my own money, but what do I know?
Why are people even comparing it to Tomb Raider? Wasn't that only on Lara herself? Not even the same ballpark as far as comparisons go. Could be wrong though, and I'm perfectly ok with that lol.