Development cost is very low for 1/12 compared to other classes. Small changes each year doesn't mean much time is spent engineering each annual change, and fairly low parts count being a pan car. Usually the diff and arms stays the same (the most expensive parts to develop along with the mold costs). The carbon plates, and rest of the machined aluminum parts are minimal and can be changed in CAD. They are then machined and cut in batches, keeping tooling costs and inventory low. Thats why you haven't really seen X-ray address the damn slop in the X12, because they would have to make new costly molds.

When you have 1/12 parts also used in F1 or WGT or 235mm classes, the costs spread out. So even if there is a decline, it doesn't take much to make minor changes each year. This was different many years ago in touring cars, when the popular cars were molded plastic tubs. They would sell it at a lower cost, higher volume, and longer production cycles until the next platform.