I'm curious about that too. I suspect it's in part about the big cities like Houston, Dallas and San Antonio, among others, where the vast majority of 6A and 5A schools come from. In those cities, they've wanted to slow down any movement toward resuming normalcy. Dallas had the interesting dilemma that they have several DISD schools that have ADM so small, that they are in 4A and 3A. But the district had an across the board limitation on when they could start. It puts them at a huge disadvantage against those in their districts and in the class, generally.
As a side note, TCCH where Deion coaches, got kicked out of TAPPS for ignoring transfer and recruiting rules. Not sure where they're playing. Maybe they are a high school independent. But they've surely started the new season off well.