I think, to beamform in the right direction you have to be able to locate yourself precisely, have an up-to-date almanach of the satellites, and a precise enough datation source. Jamming GNSS is a source of problems for 2 of those issues.

Also, the antennas on starlink dishes are still pretty small, likely to pick up some hard-to-remove sidelobes and the tech to cancel them properly might be export-controlled. You still need to be within electromagnetic visibility to jam them, though.