Why do you think the Army National Guard got all Combat Arms and the Army Reserve got the support missions ?

The realignment of CA to the Guard, and CS/CSS to Reserve took place in the early 90s under Clinton. When he reduced the AD manning, most of the CS/CSS units were cut. To maintain AD fighting strength, those units went to the Reserves (which keeps them under the federal umbrella). The Guard picked up the strategic reserve CA job. One of the reasons the Guard is CA focussed is that we are the primary line of defense for the homeland.

The Guard got the Combat Arms jobs because that is what they wanted and asked for, and what their governors asked for as well, so I guess they need to be careful of what they asked for? The National Guard is tasked with managing civilian unrest at the State level.

It's a combination of factors.

First there is the Constitutional factors such as the Army Clause, which creates and expanding and contracting Army, but does not affect the "Militia" (the Guard, which has become the de facto Militia).

The you have the Posse Comitatus Act, which prevents the Army from being used in an LE fashion, but which does not have the same restrictions on the Guard/Militias (State level forces).

Third is that you have three (3) separate entities vying for what is essentially one "pot" of money. If you had two "reserve" forces with similar missions, which shared resources, they would destroy each other. Stepping back from the Army (et al) for just a second, and look at the Services. Each is VERY distinct in their missions, though there is some overlap. The Army and the Marines don't really "fight" for resources. The Navy and the Air Force don't really "fight" for resources.... but if things were arranges just a hair differently.... we sure as hell would.

So as a pragmatic approach, CA goes to State Level. CS/CSS goes to Federal Reserve. Federal Active gets everything and can tap either as needed.