The author here says, "WordPress doesn't seem aware of what publishers need in terms of better user experience. As a consequence, the WordPress development community appears to have no plans for giving publishers what they need. A WordPress publisher opened a support thread asking why their WordPress site scored so low for Core Web Vitals (Google Core Web Vitals Fix and Google PageSpeed Insight Rank in Mobile). Google's PageSpeed Insight provides feedback as to what issues need to be fixed in order to present a better user experience as measured by the Core Web Vitals metrics."
Many of the highlighted user experience shortcomings are typical WordPress installations. The problems aren't the fault of publishers; they're built right into WordPress itself, associated with the themes and the plugins.
Common issues are things like sliders that add code bloat, forms that add code bloat, and even the new WordPress Gutenberg site design and publishing platform is inherently bloated:
|"The reason for the bloat is because it's a simple thing for developers to add all the code needed into one file and be done with it. It's not that the developers are lazy or inconsiderate. This is a common coding practice; it's the way sites have always been developed. But the Internet is evolving at this very moment to embrace a set of user experience standards that are encompassed by the Core Web Vitals metrics."|
There is a lot more on this in the original article, which you can reach by clicking on the link above!