how do things on the web fail for no reason? My experience is the exact opposite. The web's html is very lenient and if you html makes somewhat sense it will render your document.

If you're comparing legacy web code to new and modern rust crates of course it's not a fair comparison. just wait until the until the second wave of rust gui libs, it will be a similar pain of legacy code when the web industry went from Angular v1 to React. Legacy projects, outdated packages and brittle build processes, now with rust there will also be the added "benefit" of a more complicated programming language.