They got an amazing amount of mileage out of an 8-bit design based on off-the-shelf parts late in the 8-bit era. You can build a MSX-compatible machine from parts even today.

I suppose that's the power of an open standard: it's doubtful it would have flown if it was just a Sony (or Casio or Spectravision or...) design, but uniting basically every notable Japanese electronics manufacturer who didn't have a solid platform already (like NEC) made it viabl.e