Who said the E60 failed? As far as I know they (both the original, single-cab, versions and the later double-enders, some of them second-hand from Amtrak) have been very successful for decades on a number western coal railroads.
They didn't last in Mexico because the Mexican government decided not to pursue the railroad electrification plan then were purchased for: not the locomotives' fault!
As for the Northeast corridor...
(i) The E60 is, for slightly less horsepower, a much heavier unit than an AEM-7. This is partly because they were based on a freight-engine technology (not surprising, given the state of American railroading in the 1970s: look at Amtrak's early diesels!), partly because some of them were meant to carry steam generators. So they would be at an automatic disadvantage for very high speed passenger service.
(ii) Their freight heritage shows in the running gear as well: trucks like a U30C. Basically a design better for coal service than express!
(iii) Despite which Amtrak used them for many years on its heavier trains (e.g. Florida trains with "Heritage" equipment).