@kmartin in addition to the shrinking market that @kc2asb mentioned and how lucky we are to have multiple manufacturers as @rf_patriot200 mentioned, I'd like to mention that the saturation of SDR dongles and the abundance of free to low cost software for the SDRs also does not help encourage competition. Given time we will see tablet and phone apps that work well enough to actually be useful, allowing true portability using a small SDR dongle, and offering many more features than a $700 scanner.
Honestly, if I was going to design a new scanner, it would just essentially be a mini computer with some SDR chips and screen and a few buttons on the front. Everything is handled in software, and comes with a base free open source OS. If someone can reverse engineer decoding for D-star, fusion, etc, you could build a module and upload it. Same if you want to change the display.