The B-1s weren't used for several reasons.  First, their primary mission is
(or was at the time) strategic nuclear strike; Pentagon policy was to keep
them in the United States as part of the strategic triad.  Second, at the
time (January 1991) the B-1s had not yet been fully cleared for tactical
operations with conventional weapons.  Third, there was no need for them --
the aircraft already available, notably B-52s and F-117s, were perfectly
capable of the required missions, and sending B-1s over wouldn't have added
enough capability to be worth the extra maintenance involved.  Fourth, in
late 1990 most of the B-1 fleet was grounded anyway, due to engine
problems.

No B-2s were in service at the time; only a single prototype was flying.