What I’ve read is that DBX noise reduction was to blame, not tape machines, but in the liner notes, FWIW, there are no complaints to back this up.
The DBX problem -- and a crisis at the time -- is well established. There is still some problematic aspects to the original recording as @slaw indicates. A real shame.
In the liner notes, Fagan and Becker do mention "our splendid double Magneplanar monitor. system and newly acquired and fabulously expensive Audio Research D-76 tube power amps", which would reinforce the assertions about Becker at least being an audiophile.
These notes indicate how misguided they all were -- the studio should never have used such equipment for mixing room playback. I mean, really, 1 in 100,000 people have a system like that, so it's a terrible baseline for making a record. If they based their judgments on that system, well, that's just another possible reason everything wound up sounding so mediocre.