I think some folks just don't see any reason to change, as they've happily gone along on tubed tires for many successful years. Plus there is some work in understanding Road Tubeless; it's not the same, yet some folks try to think of it the same as tubed tires and have trouble.
Think about it; a guy who's been racing for twenty-five years on good clinchers and latex tubes has little reason to check out the new technologies.
I've put many thousands of kilometers on Road Tubeless, and won't ever go back to olde-tymey tubed tires. Once I understood how to fix flats easily enough (not that it happens much), I was in good shape.
I guess it's what we get used to. At this point, I'm really glad I got started with road tubeless*fairly early in my cycling.