I suppose the US helps out those who they can and when they can. Our resources arn't unlimited and our manpower isn't composed of robots. We can't just start spitting out people left and right to help all the time. With the US economy as bad as it is, helping others(whoever they are) while we helping ourselves takes its own toll.
Why terrorists attack us? There are many reasons and one is that their beliefs differ from ours. It has always been that way with some country or group of people and it will stay that way. If we struck first or we butted in where we weren't suppose to, the majority of people believed it was for good causes and we thought a little help was need. We try what we can and if it were me, I would help those in need when I could and think about some of the consequences later.