| Because it's "duplicate" or because it's never been done before.
These are the indefensible reviewer comments which can be applied at liberty to any grant application. Unlike publishing a scientific paper, where usually reviewers require some scientific justification for their negative comments, getting funding is arbitrary.
Here they are:
1) Application is too similar to applicant's previous research
2) Application does not show sufficient preliminary results to suggest feasibility.
Nearly always you get one or both of them from a reviewer. I've gotten them from the SAME reviewer, one following the other just like that list.
Of course Lamar Smith isn't going to do anything remotely sensible to help NSF, quite the opposite. Now in addition to the criteria #1 and #2 which the review committee can fling at any thing they don't like (or just happen to not be one of their buddies), NSF program monitors themselves will start rejecting applications because of some vague feeling that it would be damaging politically. The political constraints will never be made explicit on paper, of course, but they will be enforced with inexplicable "early retirements" and undenied rumors, which makes them more powerful.