Why isn't the Moon's rotation being slowed by tidal drag anymore?
Tidal slowing of the Earth's rotation occurs because the rapid rotation of the Earth carries the tidal bulges ahead of the Moon. The Moon pulling back on the near tidal bulge, in particular, slows the rotation of the Earth. This all happens because the Earth is rotating more rapidly (once a day) than the rate at which the Moon goes around the Earth (about once a month).

The Moon, on the other hand, is now rotating exactly once per month. It keeps the same face toward the Earth and thus the Moon's tidal bulges are pointed directly at the Earth all of the time and tidal effect can alter the Moon's rotation no further.