This has not been my experience with UL STPs. The standard is based on input from the STP members, not UL. UL provides some guidance to make sure the wording fits the current style manual and can be implemented. There is typically one UL representative on the STP and a UL-provided administrative support person. The UL representative is not the SPT lead. To say that UL provides a proposed standard that the STP then reviews totally discounts the work that volunteers put into the standards. With a new standard, the STP starts with a blank paper.
While some companies have a staff person whose job is just codes and standards not that many in the PV industry do. At best the typical member gets permission to attend meetings on company time, as long as that is not too much time. Because it's volunteer, meetings are short and not that often. It just takes a lot of time with all those constraints to get to a final standard. After the STP has voted to approve the final standard then it is up to UL to get it published and out to the NRTLs. The NRTLs then have to prepare testing appropriate for the standard. Then manufacturers have to decide to list their products. This all takes years from start to finish. It takes 3 years to get an NEC revision out, why think that getting a new UL standard out would take less time?