Why is the LCP metric part of the Core Web Vitals?

Google already tracked Largest Contentful Paint (LCP) data way before it became part of PageSpeed Insights or Core Web Vitals. The latter happened on May 27th, while LCP data of real users is already being tracked since at least september 2019.

In contrary to its predecessor, the First Meaningful Paint (FMP) metric, the LCP is telling a better story about the (possibly) most important element within the viewport. Possibly, as other content could still be more meaningful, but compaired to the FMP, it is clearer which element we are talking about when it comes to user engagement and tracking meaningful paints in general.