Google tells me the code to add to my page (for G+, advertising, analytics), then things like Google Lighthouse tell me don't do X, Y, Z that are all done by the code Google told me to use.
Minimise request size, leverage browser caching, defer parsing, ... they don't even minify? At least they enable gzip, Amazon ads don't even do that.
Load show_ads.js asynchronously ... well why not tell me to do that up front rather than after the fact in PageSpeed?
Google is a huge company and not every team has the same priorities is the most likely answer. It's not realistic to expect they're going to optimise the loading speed of literally everything they release.
Web best practice checks will always have some degree of false positives as well as websites are so complex.
I wrote my own Chrome extension that checks websites for best practices (https://www.checkbot.io) and had to weigh up how generally useful a test was compared to its typical false positives rate. The website for the product does pass the vast majority of the tests though, but I've only got a single website to manage compared to Google.
> Eg: https://gtmetrix.com/reports/alicious.com/RyJ575Jd
By the way, isn't some of this advice outddated?
"This page has 25 external Javascript scripts. Try combining them into one."
"This page has 3 external stylesheets. Try combining them into one."
This is obsolete with HTTP/2 because files can be downloaded in parallel. Combining the files will also increase the weight of pages that don't need every file.
How about just the things that get duplicated on more than 10Million websites?
>By the way, isn't some of this advice outddated? //
Yes, the link was just supposed to be broadly indicative. Google signpost Lighthouse as the primary tool now rather than PageSpeed I think but you can't link to that on the web. [And even Lighthouse has false positives, but that's not the issue here.]
> This is not something improving the vm can fix. There just is no competition so that customers could send a feedback signal saying that performance is unacceptable.
I think that's part of the reason Google made AMP: they don't allow arbitrary JavaScript scripts because it's not practical to get all websites and all developers to optimise JavaScript usage. Likewise, the amount of CSS code allowed is strictly limited.