Your position is based on the premise that all things are constantly improving, which I do not ascribe to. Although it is part of many companies marketing strategy that they are constantly evolving toward perfection, many of us don't view it that way.
The 'evolving' is partly a function of the manufacturer having a need to keep his brand before the public eye. (Same with some audiophiles who keep themselves before a social media audience by continualy changing to the latest products.)
Granted there are occasional improvements in materials and small part components, such as capacitors or printed-circuit boards. Sometimes use of these get slip-streamed into a build and sometimes they are touted as a new model. Sometimes features of a higher level model get passed down the line to other models. Typically product roadmaps are planned out for several years.
New products mean new advertising and reviews. In general the audiophile press does not cover products over a year-or-so old.
Plenty of market churn there is.The manufacturer who gets it right early on is at a disadvantage.