I used Scientific Word to write my dissertation and my first academic papers. It was a great piece of software in the late 1990s, at least relative to the alternatives, which were writing .tex files yourself or typing in a word processor. I have a coauthor that still uses SW.

I can't say this is surprising. I moved to LyX long ago, and then after markdown became popular I ditched LyX and went with that. There are lots of strong alternatives today. There probably aren't many people willing to pay for something they can get for free, that they already have, or that doesn't provide features for collaboration.