USA needs such a large military for US economy to stay alive. As soon as you release your "loving" tight embrace, your "friends and allies" will immediately choose freedom and get away from your sphere.
Europe will go to Russia and be free happy and wealthy...will quickly solve their migrants problem; Middle East will stop burning...
And all that would weaken dollar. As a result USA will became just a country like all others...one of the players playing same equal rules. And it will kill USA as you cannot play fairly.
So until you have large military you keep your today's global position even though your military is not effective against strong opponents.