Field artillery carriages are not all that hard to make, one part at a time, but they have lots of parts and you need to be both a wood worker and a metal worker to build one. The metal parts are mostly blacksmithing stuff, and the wheels have so many duplicate parts that you just have to make fixtures to make them all the same. But most people won't spend the time making the fixtures, even after being told that it will take less overall time to make the fixtures and make the parts than trying to make each part separately.
So nothing gets done past the first few parts that take longer than expected.
