Tuning adapters suck for the same reason CableCard as a whole kinda sucked. Because the cable industry as a whole wanted them to suck. Ever notice how their own boxes never had the same problems, even during the time they were forced to use the same CableCard interfaces? Or how variable the support was between providers, with some providers happily shipping cards to consumers and offering self-service interfaces to activate them where others would insist on a truck roll and scheduled appointment (with standard cable company timing)?
Look at the same concept as implemented in Europe. Over-the-air, cable, and satellite television all use variants of the DVB standard. It even has an IPTV variant, though I'm not sure how widely it's deployed in that context. There's a standard interface for a service provider's encryption solution. Any consumer can use any compatible device with any television provider, and it works great.
For whatever reason (read: doesn't benefit the right companies) in this country we have a history of looking at problems Europe's already solved and saying "nope, we can make something much worse for consumers". See also GSM vs. CDMA and the fact that Verizon still insists to this day that they need to individually certify each device while the majority of cell carriers on the planet happily work all day with whatever phones happen to be compatible.
It's easy to be compatible if you want to be compatible. What these companies try to avoid saying outright is that they don't want to be compatible.