So the reason for that was that Apple was of the legal opinion that GPLed software was incompatible with their OS. Since they didn't have process boundaries at the time, all code running on the system, even the OS was basically linked together in a big blob. Apple thought (incorrectly) that allowing any GPL software would mean that they had to GPL their OS, and were vehemently anti free software.

I think under those conditions, the FSF's boycott was fair.