It's because large, directive antennas are still 'dish' style and have to be mechanically pointed at the target (Earth based DSN receiving antennas). That point

It's because large, directive antennas are still 'dish' style and have to be mechanically pointed at the target (Earth based DSN receiving antennas). That pointing causes vibrations and potentially a shifting center of mass. Phased arrays allow beam pointing without mechanical movement, but are very expensive for large high gain antennas.