I don't think that they have gone out of fashion at all, just look at all the custom jobs or the posts on this forum or the other place.

What has happened is that due to the complexity of the design they cannot be made for the $600-700 that Savremchester sell their guns for.
The largest consumer nationaly of guns buys their firearms very much on price.

It takes over 700 seperate machining actions to produce a true Mauser action, it is written in a well regarded book on the guns that over 700 dedicated machines were used in its manufacture.

A Rem 700 for example can be made on a lathe and a milling machine only.

Regards