It's a really good question why Casio didn't continue making synths after the 80s. It's possible that the entire CZ-line was intended to be a one-off response to Yamaha's breakaway success with the DX7. After the CZ-line, it looks like Casio tried to keep up with Yamaha for a few years, but exited the market after Yamaha launched the SY-line. From what I understand, the CZ-series were great sellers then, but even with all of the nostalgia they'd never move large numbers now.
For what it's worth, Yamaha aren't particularly nostalgic about their cult-classic synths either. I guess that from their perspective, the DX7 and CZ-101 were already obsolete within a few short years. By 1990 the sound had already become quite dated, and technology had moved on. Now that they've become popular again as a cult-classic, the margin just isn't there anymore because of the market share of software, or cheap independent FM/PD synths.
Shameless plug, in case anyone is interested, I've done some work reverse-engineering some of these synths:
- https://github.com/ajxs/casio_cz101_rom_disassembly
- https://ajxs.me/blog/uCOM-87_The_Strangest_Architecture_Youv...