You will inevitably need to use the website at some point to find past discussions about such and such. And, somehow, all mailing list software seems to have this kind of web UI.

But also, part of the problem is the use of email lists. Or rather, specifically, plain text emails, because they contain pre-wrapped lines, and users often assume monospace font. You can try to reflow, but in general it's not possible to determine whether any given line break is there because the line just needed to be wrapped, or because it's actually meaningful (for code, diagram etc).