Why most on-page checkers stop too early
A lot of on-page SEO checkers still behave like a form validator.
They check whether a keyword appears in the title, whether the description exists, whether a heading is present, and whether the content hits a rough word-count threshold. Those checks are not useless, but they do not answer the harder question. Is this page actually the right answer for the search intent it is trying to win? That is usually where page performance is decided. Surface checks can tidy a page. They rarely explain why a page still feels weak in search.