This trend is accelerating; small, one person companies founded near the beginning of personal computing are shutting down. Others that come to mind are MicroCAP for SPICE simulation, WRCAD for IC layout.
Is it due to the market, or the owners are retiring/giving up?
Also, without looking at this in general, I wonder if it's hard to compete with Mathematica which is ~$1000 for a professional license (very reasonable in the industry compared to most others) or free on raspberry pi with free or near free for most students. Also, there is open source software as well that could eat into their niche.