The state-of-the art Mauser, which command high $$$ involves hand fitting and wood quality, and it's what makes the value go up very fast. As an example, all the metallic parts are fitted and polished (filing, sanding, honing, lapping etc) by hand. There is a lot of time and experience invested in those rifles, every parts are file / stone fitted....
You must see it as each rifle is a one of a kind for all the art / crafstmanship / material involved.
On the other hand, you have all those pre-WWI interwars, and WWII rifles which were more utilitarian - mostly used and owned by the upper classes or rich "farmers", the nobles using the more fancy ones - going for some good money too. The main thing about them is that they're still accomplishing the task they were designed to, and they still will for many decades in the future.... and that there are not so many around.