Likely because they don’t work exactly like scanners, such as scanning more than one system.
I agree 100% That's why I haven't bought one myself, and I remain content with my three Unidens. Over the years I have found simple little things that make them work better with Simulcast systems and for the most part I'm satisfied. That's not to say I'd like them to be better, but as the saying goes, as bad as scanners are, they're the best we got!
I started with simple 8 channel scanners that used crystals. As technology advanced/improved I kept pace with it by selling what I had, and buying the latest and the greatest. Yes there were growing pains along the way, but that goes with the hobby. Many of the people complaining about today's newest scanners don't have an appreciation of what it took to get where they are. If you expect them to perform 100% perfect, you should problem seek out a different hobby. Scanners are a work in progress. As improvements are made, new firmware is usually released. As more significant additional features are engineered, they are made available.
All the complaining in the threads isn't going to change a thing. Uniden, and Whistler can't pull a fix out of their hat. It just isn't that easy. Do you honestly think manufactures just delay things to irritate customers. I think a lot of people do not show Paul and Wendy the respect they deserve. Yet at the same time they try to push them harder and harder for a fix. If they had a fix, you'd have it. If it take more time, and it's possible you get it, but not before. Some people on RR act like spoiled children. Perhaps they are!
belvdr, to be clear I'm not directing this at you.