Sure, but an individual website may use only a few of those standards. Ladybird devs will pick a website they like to use - Reddit, Twitter, Twinings tea, etc. and improve adherence to X or Y standards to make that one website look better. In turn, thousands of websites suddenly work perfectly, and many others work better than before.

Ladybird is largely conformant to the majority of HTML standards now. It's about the edge cases (and where standards aren't followed by websites) and performance. This isn't a new project.