I was involved in SEO related projects some time ago. Not that I’m an expert. I’ve heard google understands that the site is a search engine and does not index it. However it should be smarter, like do not index SO’s search pages, but do index question pages - because the original content is there. SO might have ran out of crawl budget which Google assigns to each site, and/or Google prioritises fresh content. But I agree with the sentiment, what we know as SEO is nothing more than playing games with Google indexing algorithms, based on rumours about the recent changes in it, or improving page performance beyond reasonable boundaries. The other day I was looking at apple.com internals and spotted a few things which we were “fixing” on our pages. I asked SEO experts “what is the point of doing X, since there are examples of a well indexed page having that same problem?”. And the answer was like “when we will be as big as Apple…”
