[chocolatkey]

I don't like it either, but the only way it is technically feasible to support the full potential styling/markup of an EPUB is to use a browser engine, and therefore electron is a logical choice. Can your specialized EPUB reader support MathML? Or vertical-ttb text?

[Finnucane]

Just this. Epub depends on the same tech stack as the web. So, either you use an engine that supports that in full, or you are going to be missing pieces of the standard. Which means that most other reading software opts for missing pieces of the standard.