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.