No expert on this by any means but maybe the cost of developing a recovery vehicle
on the M1 chassis was not supportable.
Correct me if I am mistaken but it is my understanding that the M88 uses the same chassis
as the M1 but is radically different as to engine, drive chain, etc,etc.
Not to mention all the other specialized stuff that makes it a TRV.
Perhaps there was just no money or maybe it's a pork barrel thing, certain politicians didn't
want to lose the industries from their states.
Of course, it could be an effort to preserve the capability also, I don't imagine that there are
too many places left that can still make large scale steel castings, I.E. tank hulls and if presented
with a conflict that truly stressed the military supply chain it might be handy to have such on
a "back burner", if you will.