It's normal in all industries, and in fact quite smart, to roll things out over time in order to capture data and feedback, train additional staff, refine procedures, etc before another stage of rollout.

This idea was of course first pioneered with software development (alpha test, beta test, etc) and then adopted by the broader world. We even see it now with restaurant soft openings etc.

I'm sure at some point it'll be available at all airports, but given how fast government moves, it could take a few years.