Why don't the developers develop a stable ROM for my device? They have stable ROMs for similarly-named devices from the same manufacturer, even ones that came out after my phone. If the devices are similar, and there's already a stable ROM for one, why is it so hard to make a stable ROM for mine too?
Two devices with similar names, like the Sony Xperia Z and the Sony Xperia Z1, don't necessarily have the same kind of hardware. Sometimes there are even devices sold under one model name, such as the Samsung Galaxy SII, where the variants available in different countries have completely different systems-on-ship (SoCs) and other different hardware.
Devices with different hardware need different drivers &c. and a lot of system integration work that can't be shared between the two. Testing an unstable release to find the problems with it is very time-intensive, and of course can only be done on the exact hardware being targeted.
Since Cyanogenmod is made by enthusiast developers, rather than by people who are paid to do it, support depends on having an interested community of people with the system integration knowledge needed, and enough such people having that particular phone to run and test the ROM images.
It may be that there's not much more work required to support your device, but the people who might be able to do that don't happen to have one. Or it may be that none of the porters who have your device have enough free time right now to dedicate to testing and fixing ROMs. Lots of volunteer projects like this are stopped when members have children or start new jobs.
Even if you don't have the necessary knowledge, there are other ways you can help get your device supported. You might be able to help by contributing some money to support the developers, devices so that more enthusiasts can spend time working on it, or by testing and reporting bugs to make the process faster. If you ask the Cyanogenmod community how you can get involved and what would help, I'm sure they'd respond positively to that.