All US Records are Now Motor Glider Records
One problem I see here is that this policy is being applied to both US national and state records. US state records are more of a "for fun" thing to encourage pilots to increase their achievement level. Since they already have no direct analog in the international community, I'm not sure why it was deemed necessary to implement this policy with regard to state records. All it does is eliminate opportunities for aspiring pilots to be recognized at the state level.
I'm the Utah State record keeper. In 2016, I approved 10 records for non-motorgliders, and 3 for motorgliders. This ratio has been more or less 3 or 4 to one in favor of non-motorgliders for years. The assertion that non-motorglider records are no longer being actively pursued just isn't true at the state record level.
By the way, in 2016, the successful applicant in the motorglider class would have had no chance if forced to compete in the open class. Had it been implemented in 2016, this policy would have only had the effect of eliminating recognition for the motorglider pilot.