Originally posted by biz-engineer A large used market for a lens mount is good for customer but very bad for a camera business, that's why Canon, Nikon etc.. change lens mounts once every decade or so, to avoid the used market becoming the dominant market for their brand.
Let’s not get the facts twisted. Nikon F mount was quite long lived, longer than k mount actually. The F mount was first introduced in 1959, and Z mount was not introduced until 2018. Just like the K mount (1975 to present), the F mount had evolutionary changes over time but kept reasonably compatible. The one major difference in their backwards support was dropping screwdrive from their entry models.
Canon too kept EF mount longer than a decade; introduced in 1987, the RF mount came on the scene in 2018. The FL (1964-1971) FD (1971-1987) mount and the R (1959-1964) mount were shorter lived, thought the FL lenses worked on FD mount cameras with limited functionality (stop down metering).
Pentaxes easy use of m42 lenses is nearly unique in that it gives easy access to lenses all the way back to 1949! True many mirrorless designs offer easy adaptation of the manual focus lenses of many brands, but only Pentax offers this level of continuous lineage of glass without ditching the ovf. However, let’s not cast Nikon and Canon in the role of swapping every decade…