I think it’s partly a legacy issue related to blades which can warp in the quench or with conversion of retained austenite over time, partly a superficial understanding of what qualities are actually desirable in a cutting tool, and partly a valid desire to have a competently made tool.
My understanding of retained austenite in steel is that it can convert to martensite with time or from being worked. This means that the crystalline cubic structure in those areas would change to a tetragonal structure, and induce some degree of dimensional change and warping.
I’ve heard of carbon steel traditional knives from well known manufacturers taking on banana bends in their blades over time, while just sitting in the box.
I’ve personally had traditional knives which have warped blades in different directions. Some makers I won’t name always
have warped blades.
Spyderco cryo most of their blades anyway, which among other things results in no measurable RA, so this is generally a moot point with their knives.
It can also be an indicator of attention to detail by the maker. If they haven’t paid attention to some easily observable qualities, then have they potentially cut corners on things which you can’t see, like the heat treating process?
Then there’s the ‘pocket jewellery’ aspect. There’s about a zillion tabletop Youtube reviews out there where people discuss things like blade centering, ‘fidgetability’, cosmetic fit and finish, and ‘sharpness’, without ever actually zeroing in on the things which are more important IMHO, that relate to the knife’s effectiveness as a cutting tool. Things like blade geometry, behind-the-edge thickness, edge angle, ergonomics in different holds, sharpenability, likely best uses for the knife, any info on heat treatment, what the designer was thinking of etc.
Personally, I have never noticed any performance issues in use from a blade which is slightly off centre. In Spydercos I can generally centre the blade with judicious screw adjustment, or I just don’t care enough to do it.
Also, if you’ve been trained in how to assess blade straightness, it’s actually very rare to see fixed blades in particular which are actually laser straight. I was lucky enough to be shown how to assess blade straightness by Murray Carter so I could better select knives to buy at the Seki Knife Show a few years back. All
the knives we randomly selected to practice on exhibited slight bends and asymmetry.
At first I practiced the skill at every chance I had. Now, I rarely do it, unless I’m considering buying a custom knife at a show, and then I do it very surreptitiously so as not to offend the maker if I then choose not to buy the knife. Once you see it, you can’t unsee it, and I figure if it is so minor that it doesn’t affect the use of the knife, then I don’t care about it.
Just my opinions, of course.