I believe the reg used to say 12 months, and they changed it to 24 months a few years back, for tow pilot currency.
Part of initial tow pilot training includes flights in the glider, so was the reg designed to remind tow pilots what the other end of the rope is like?
Hard to say their initial thinking.

I find that you have to watch glider rated tow pilots, they tend to go all year towing and forget the glider flights needed to maintain tow status.

As to student pilots, there is a process ing worked to let students apply for their certificate up to 6 months early. I think Ken Sorenson was looking for instructors that had students between 131/2 and14 to test the updates to the FAA web site.

BillT