Well, we know Pitt and Jolie have plenty of love for New Orleans given their involvement post-Katrina. I don't know why they aren't more involved. It's a much dicier political issue in some ways because this wasn't a natural disaster, this was a massive screw-up by a corporation.
Of course, one could easily argue that Katrina was a government screw-up given the issue with the levees, but at least on the surface, it fell in the disaster category.
In any case, the fact that it's, arguably, a dicier political issue shouldn't matter. Maybe -- as Liz and I posited before -- they are waiting to see how things play out with BP containing the problem before they get involved.