They are using up those visas to merely to fulfill demands of their US clients. This is a fairly straight forward case of demand creating supply. It always has been. We have heard this whining before. Good for scoring political points but not much more than that. As for an explanation I am sure Infosys and Wipro would be more than happy to talk to the US Senators and make their case. I'd love to be a fly on the wall in that conversation (or check it on C-SPAN perhaps :D)