This was a model developed at the behest of BNSF, in order to get a reduced cost AC traction unit for non-coal service (primarily intermodal) where AC traction 6 axles are unnecessary overkill. FEC has long ordered units using specifications of larger roads in order to keep their prices down, and being a pretty flat operation the A-1-A arranged AC traction engines were a perfect fit.
As for GE having "little success" with this product, BNSF bought (between ES44C4s and ET44C4s) a total of 1,465 units so far - you can count on the ET44C4 to be the lion's share of future orders too. It's one of the main reasons GE's new factory capacity was built in Fort Worth, TX. So much for the "little success" GE has attracting orders for this model.