Why a page with an On Page A grade has a less good rank than a page with a F grade?

[Amadeus_eBC]

Why a page with an On Page A grade is ranked 17 in Google when the home page with a F grade is ranked 9 ?

Thanks

[PeterM22]

onpage seo is only one of many factors search engines use. Google is getting better all the time at ranking sites for things that are highly relevant but don't have good onpage optimization for a particular keyword, but maybe is well optimized for a synomym..like a page may rank for "autos" when it is not optimized for "autos" but is for "cars".

[BenFox]

Peter is right. On page optimization is only one part of the puzzle.

For example if your homepage even mentions a term it can sometimes outrank a more relevant page on the interior of your site.

[bradkrussell]

You could also have 1000 links with anchor text associated with a particular term pointing at the page that has been graded F, and only 1 link to the page that has been graded A.

Google is obviously going to give the page with a lot more links more authority.

Like the others said, on-page optimisation is just one part of the puzzle.