The Army is living in the past, pre-1960. In my father's generation, a high-school diploma actually meant something. It was a certification of sorts and was a 'real' achievement. Graduating high-school meant you can read and write on an adult level and can do fundamental math.
Today, a high-school diploma is nothing at all. A large percentage of 'American' high-school graduates cannot read or write, they cannot do math, and they have no concept whatsoever of civics or history. In many parts of America, a high-school diploma is a 'political issue' based on the status of the school and the race of the student. He didn't show up to class ... and he did no school work ... he cannot read or write ... but he "deserves" to graduate because he has a hard life.
This decision is a mistake. All recruitment and placement should be based on the ASVAB. That is a real factual measure. Having a high-school diploma does not represent a person's ability in any way whatsoever. Today, having a high-school diploma is completely meaningless in terms of measuring the ability of a person to function in a workplace. It has no meaning at all.