> Especially considering what they want would rather be specified as a parser for generating URLs from user input, and not to simply demand every tool interacting with URLs to be able to parse malformed URLs.

The goal of the URL standard isn't to generate URLs from user input (for example, the browser address bar is out-of-scope), but instead define how <a href="foo"> in HTML (or, rather, more generally, {http://www.w3.org/1999/xhtml}a@href from the DOM), url("foo") in CSS, Location: foo in HTTP, and similar get parsed. There are large parts of this that the web relies on undefined error handling around this, which makes it worth standardising somewhere (as browsers cannot practically drop it, and most web content is targeted primarily at browsers, hence if you want to be compatible with the web you need to be compatible with browsers).

I'll also point out that the WHATWG scarcely exists: as a venue there's almost no formal organisation or high-level plan, it largely working on some shared values, and as a result there's a fair bit of variety between different groups of people working on different specifications where some take those values to further extremes than others.