I asked this question in the WTB forum, but I think it may deserve its own thread.

Why were all the display case bezels snap on/off and not threaded?

I would think that it was simple economics. There seems to be a lot less metal in display cases compared to standard cases. In order to be threaded more material would be required which would then add the extra cost of the metal and the cost of the threading in manufacture. Since there was, I assume, no intention to market them to the public the added cost of threading would not be justified.

Interesting to see some of the prices they go for these days though.

If you consider the Dueber Hampden display cases as an example of the display cases evolution you will see the original D-H display cases seem to go from a plain nickle case body but with hinged bezels to a nickle case body with snap on bezels and of course Mr. Duebers ultimate money saving innovation, no bail on display cases. Further the metal seems to be a bit thinner on the latter cases. This is not to say that variations do not exist. I have some D-H display cases with brass or gold platting, an early case with a private label movement that has a bail, a case with a hinged front and snap back and I seem to recall one lightly threaded 18s case. John Dueber was not one to waste a penny and his display cases reflect the idea that they are to be used for display only.