Well, users would be happier with websites that showed fewer ads and had fewer tracking JS scripts slowing down the website. Will Google ever rank by that metric? Google is slowly but surely becoming an ad-infested link-farm kinda website, one they used to ban in their search results not too long ago.

> it indicates that users are happy with the result

Doubt. Especially "time spent on website" primarily indicates that the user didn't quickly find what they were looking for.

You'd be correct in assuming that it's a good indicator if it wasn't gamed. Since people believe that it's a ranking factor, they'll do whatever they can to increase it. Shitty SEO texts that go on and on without actually saying anything, breaking the back button, adding exit intent popovers, you name it, it's out there. All heavily increasing time on site. Are the users happy? Do you prefer a 5 sentence page that just plainly answers your question about some topic, or do you want a twenty paragraph novel that maybe, possibly somewhere includes the answer, but you need to completely read this opus magnum first?

Time spent on website?

Is that why answers are always buried in long articles or walls of text?

Seems a horrible metric.

Google uses that to a limited extent - if someone returns to the search results within a few second of clicking a link, the link wasn't what they wanted.

Publishers definitely use it more heavily.

Time spent on a website is an interesting metric. I am curious if there are studies linking it to happy users. I would guess there are some interesting findings after you remove immediate bounces from the data.

Time spent on website is more time spent looking at advertisement. The last thing an advertiser wants is a user finding their answer quickly and closing the tab without engaging with any advertising.

I have heard the AMP team is/was part of the search department.