Armed services don’t have enough recruits, so they want a bigger pool to chose from. If every kid has to take ASVAB, then they have a much bigger pool of possibilities, including being able to actively recruit better suited people. The other point was to expand jROTC, to do exactly that.

I had no interest in the military but took ASVAB thinking of it as practice for SAT, which I did care about. However the tests were different enough to not be good practice, plus then I was constantly recruited by all branches. I expect they want to be able to do more of this