It might seem insane to the parents but you need to remember that the district has about ~10,000 kids in each grade. So for 1st, 3rd and some of 5th, that is close to 25,000 kids who need to be evaluated for the program. This is in addition to all the kids who get tested privately. There are only 3 or 4 people in the TAG office and they have other responsibilities.
I think that they try to release the OLSAT test results after they get the teacher assessments for the kids who qualify so that they can provide the TAG identification in the same letter. That requires multiple teachers from 130 schools to respond to the questionnaires.
It's a huge undertaking and should really be decentralized.