I'm guessing it's a liability reason that you're not allowed to teach it in the pool for the refresher?Refreshers can also be done in Open Water, but there are few skills that could only be practiced in the pool within PADI standards.
The one notable is that even though the OW student originally practiced a CESA in OW, we are NOT allowed to include it when doing a Refresher in OW, only in the pool.