> older pages might not be optimised for current web vitals metrics
For news sites that's unlikely to be the reason.
Generally speaking, old online pages are the same as new online pages, because all the article content is just pulled from a database, a CMS. All the rest of the page (menu, ads, footer, etc.) is modern and kept up-to-date. It's not like an article from 2007 is using the same HTML that it was in 2007.
Just because on your personal blog, you'd left old blog pages on some ancient clunky Wordpress (?) version, that isn't how large publishing sites operate.
It’a not that simple. Older content might not have webp images variants available, or styling might be optimised for newer stuff and cause old pages to reflow, and many other things like that.
Key web vitals change over time and it’s often a mix of content, styling and scripting that needs to be optimised to fix CVW issues. Revisiting old content and rebuilding old assets might not be worth it.
I’m not talking from a perspective of maintaining a personal blog, but a product web site that currently gets about 1.5 million visits from organic search per month. It’s not CNET, granted, but not a trivial site either.
A large website wants to have its current content cached as much as possible—ideally very few users should be hitting the CMS directly—but it doesn't make sense to cache content from 1995 on the off chance that today is the day someone needs it. In fact, to speed up database performance on your current content it may even make sense to store your archives in a different, less beefy database.
However, if Google penalizes slow performance on any page, even archives, these strategies could damage your search rankings even for your current content.
A lot of CMS software allowed you to add custom HTML, so there are hundreds of thousands of images with "float:left" hardcoded among many other deprecated HTML stuff that Google Search doesn't like.
For news sites that's unlikely to be the reason.
Generally speaking, old online pages are the same as new online pages, because all the article content is just pulled from a database, a CMS. All the rest of the page (menu, ads, footer, etc.) is modern and kept up-to-date. It's not like an article from 2007 is using the same HTML that it was in 2007.
Just because on your personal blog, you'd left old blog pages on some ancient clunky Wordpress (?) version, that isn't how large publishing sites operate.