I always understood it as they don’t parse the actual details of emails (the body) to generate an add profile. It doesn’t mean they don’t track what websites you’re visiting whilst logged in though.
My guess to this is that it’s not accurate, for example email chains, or someone mentioning something that you have no intention of buying. As the email body is very unstructured it would be quite difficult to interpret whether those keywords should be added as an interest, having said that, with advanced AI that can parse context of a sentence they may just start doing that again if they can with accuracy.