I have NO specific information. A few generalities occur, however.
--They were built in 1995, and (at least initially) were in high-mileage service (think: Santa Fe main line): lots of locomotives have lasted longer, but 15 years is conventionally stated as a lifetime for diesels in main-line service.
--They were the first EMDs to have the 16-710 rated at more than 4,000 hp: 4,300 is now standard, but maybe there were issues with the early versions?
--DC traction motors. BNSF has lots of C44-9W (and ES44DC), but they have the good GE 752 and not wimpy EMD traction motors (grin!). BN was the first big railroad to go for AC traction motors in a big way, and in the past few years seem to have decided that four AC motors are better than six DC for their mainline non-coal trains. So maybe they see the SD75 as representing a technology they would like to phase out?