Decompiler space probably has a few tens of millions in revenue yearly, yet writing a good decompiler is quite a lot of engineering effort, and you are not going to spend tons of money and effort to capture a measly 10m market, you'll rather be the next uber type thing that targets a much bigger market.

Hence HexRay can get away with not doing much and just collecting license fees from existing customers yearly, as there isn't a better alternative anyway.