While that would have been a good idea, I can understand why they didn’t. If they had people preorder now before making anything, that saves the problem of if the unis fell flat, so you’re right in that thinking.
The department likely can’t (contractually) sell merch themselves so they would have to get Follett or whoever has the stadium sales on board. The logistics of that and what Follett would want to do or be capable of handling would be a question (although I think they have the infrastructure to handle it even if they didn’t get another vendor involved). You run the risk of ruining the surprise, which had this leaked out this summer might have not had the impact were getting this week. Then how many different styles do you offer for preorder, and how many is a minimum order before it is worth the extra effort it would take. Then does the athletic department and/or Follett have the personnel to handle all this in the first couple weeks of school.
That’s just a simple analysis though. Now they could now allow some or all licensees to start printing this stuff like they did with Phi Slama Jama and the True UH collections. If the demand is there, while it might take a bit longer, the merch will be available with less time involved from the athletic department and with the vendors taking on all the risk of merch that can’t sell. UH just collects their royalty.