I think procurement for Navy Air training aircraft only permits one bullet in the chamber at a time - first it was T-6, now its TH-73. T-45 can withstand a lot of maturity/upgrade in its lifecycle. Look how long it took USAF to get TX up to have a roadmap to replace T-38. There are half the number of T-45's than the number of TX (T-7A) to be procured by AF.
With the engines shitting themselves five times now, the T-45 definitely needs the accelerated timeline and priority. Numerous lengthy groundings of part of the fleet (or the whole fleet) have multiple downstream effects. And that is without even mentioning the obvious safety concerns.