> Why didn’t Sony become a major PC manufacturer after this?

I remember reading about it in magazines when it launched but at ~$1500 for the base model at launch (without monitor) and still ~$1000 18 months later, for consumers it just couldn't compete with the $600-$800 Commodore 64 and Atari 800. In 1983 >$1,000 was a non-starter for amatuer hobby users, plus there weren't many game titles for it.

While CP/M was popular with the early IMSAI / SOL / S-100 homebrew hackers, it was never very relevant for most mass consumer hobbyists. CP/M was really disk-centric and in the early 80s floppy drives weren't within reach for the '2nd Wave' broader consumer hobby market. We got our first computers (C64, Atari 800, TI 99/4a, Radio Shack Coco) envisioning cartridge & cassette usage plugged into a TV we already had through an RF modulator. If you could afford it, the component RGB output of the Sony would certainly have looked incredible but in the early 80s most consumers were still a few years away from even seeing their first RGB monitor in person. No local store had ever even had one on display, so we didn't really know what to make of it. To us, Composite Video was the esoteric "better looking" output vs RF to your old TV. :-)

The SMC-70's price and capabilities were a better fit for business users but by '83, MS-DOS and "PC-Compatible" were clearly 'the future' for business users and CP/M was on the way out.