Pellet rifles offer excellent marksmanship training at a very, very low price vs. the cost of rimfire/centerfire ammunition. While they don't produce the recoil or noise of a centerfire rifle, they still develop things like stance, sight picture, breathing, etc. etc. very well. Airguns also aren't quite as loud as a rimfire rifle in most cases, though some can be fairly noisy. It all depends.
People who are buying the more expensive airguns probably just want a high quality and accurate rifle because they already shoot airguns and know how fun they can be!