Comcast cares about the issue because these requests are costing it money. But if the government should compensate them (as they do for phone tapping), no further protests would occur.
Recently, they've had trouble with certain law firms actually paying these fees in a timely matter which prompted them to start fighting these law suits.
At the rate these suits are being filed, they've really had to staff up. You can't hire someone from a temp agency to work in your legal department.
If they could do these things in secret you might be right, but the subpoenas are public. And their objection is even more public.
I love that the reaction of their customers drives their policies, that's exactly what I want in a company.