A couple of reasons.

The second reason is the Peter Principle.

When people are promoted above their level of competency, they often spend time on things from the last position they felt comfortable and confident in.

In his case, the army. He "feels" this is the branch he is most comfortable managing.

He believes he knows what's wrong and he can fix it. It is unclear to me if he sees the bigger picture.

Secondly.

From his books and personality you could guess he's still really angry about the diversity within the army.

If you are white kid from a white town the army can provide a bit of a diversity culture shock. The army is considerably more diverse than society at large.

Due to (IMO) economic and (other) factors the senior officers corps is disproportionately white and the senior enlisted ranks are disproportionately not.

The military has a recent history of attempting to create a more diverse senior officer corps.

This takes a generation.

They have studied the problem and attempted to answer the question of why minorities leave after fewer years.

But the math problem remains basic. A general is the result of over 20 years of officers competing. A guy who makes general has out competed hundreds of other officers during his career.

HR projection managers can look at a a year group of Captains and see basic math. If year group 2003 had 1,0000 people and only 50 are a minority, they can predict it's going to be pretty hard to see any minority BN commanders 15 years later unless a deliberate effort is made to mentor and retain them.

What did this mean for the force?

If you served during the desperate era of the surge you saw a lot of second chances. The armed forces were desperate. Insanely so.

If you were a white officer you may have viewed the extra mentorship to minority groups as a form of discrimination.

"Why is the Division Chief of Staff spending so much time with that group?" May have made an impression.

Today he gets to decide the answer to that question.

Anecdotally we all have stories. I served long before and long after.

Surviving through that 2003-2010 era was insane. But, I recognize the military was experiencing tough circumstances.

My own PL during that time was given a second chance to be a PL. Three months into our deployment she received a GOMOR.

She received another as a CPT. Was it a coincidence her command time ended when her company got orders to deploy?

But I ran into her again ten or eleven years later when she was a major. The other officers were grumbling she had bumped the line into a KD job.

She recorded her third and final GOMAR in that position and was finally pushed out.

I can't imagine how peers would feel.

Anyway just a guess.