At a guess I'd say that the spec wasn't quite competitive enough at the price it was pitched.

Consider that the C64 was also launched in 1982 for a much cheaper price and was available in non-NTSC regions too, so would have had a bigger software library available to it.

Many people can put up with less convenience with peripherals if you're paying an order of magnitude less up front.

Even the software on cassette and 5.25" disk would have been so much cheaper to distribute than the newly launched 3.5" disks (which were much better).