Because vacuum is vacuum. Or rename VACUUM FULL to something else, so that
no one can reasonably assume that:
1) a command with VACUUM in the name should update the last_vacuumed field,
or that
2) VACUUM FULL should be done often, since FULL is seemingly better than
not full.
Proposed new name: RECREATE TABLE <table_name> [ USING <index_name> ];
The USING clause added since CLUSTER is really a sorted VACUUM FULL,
I'm not wedded to the name RECREATE TABLE, but am wedded to the fact that
VACUUM FULL is a horrible name for what it does.