I believe you, but that might be similar to a test in a Petri dish versus a test in a living mammal. Do you have examples of the type of case you are referring to? I could be making a wrong assumption about your comment. Aren’t snap cases made of TPU? Theirs a lot I don’t know about manufacturing.
My snap cases are typically smooth without rubberized coatings, so in an out of the pocket is a breeze where the ones with a high coefficient of friction tend to be hard to put in and remove from a pocket as well as doing the lint harvesting thing. The snap case is not bulky or intrusive of the buttons or charging connection areas.
I’ve had some epic fumbles with my phones in snap cases and I always am amazed that their’s no apparent damage (but in my head I’m convinced there is something newly broken inside the device that is hard to detect).
Also, it seems that Purism / Librem could outsource the fabrication of cases with on-demand production and reasonable pricing through a place like this:
https://www.carbon3d.com/materials/