Because the answer to a blown out 25 year old part is....another 25 year old part.
I'm guessing at this age, even the basic power semiconductors used are gonna be hard to source. Add to that your control cards, contactors, etc etc etc.
Retrofit? Sure. Got the money?
I suspect the recent rebuilds and retrofits and more rebuilds of SJ and Green cargo's fleet is chasing the same issue - i.e. that the parts supply for the locomotives is simply drying up.
If it's cheaper to buy/lease/whatever a few sprinters as a tack-on to Amtrak's order, than why the heck not? Too powerful? Who cares, it's an electric. It uses what it puts out. Just dial it back (though, why?)