Yeah, because that small pool of people would justify keeping an entire manufacturing facility open to produce a Mac nobody else was interested in. Nobody wanted a black & white computer in 1993. And Apple couldn't justify charging the same amount for one as a new IIfx from which it would cannibalize sales as well as from the Quadra, nor could they afford to upgrade the technology to charge more due to the shrinking market. They did continue selling it for as long as it made financial sense after they announced it was discontinued. And nobody wanted a 9" Black & White monitor if they could afford better in 1993. The SE/30 was done after a healthy 4 year run. The entire form factor was abandoned in favor of the Color Classic, which due to the small size of its monitor did not sell nearly as well as the 520 released at the end of the year. It's just that simple.
Its the same reason Apple no longer sells the Cube despite the small niche market that would love to see it continued to have been made.