a lot of people that call themselves SEOs are oblivious to this stuff.
Many people are now SEOs without having ever built a website. They have few technical skills. As I said above, the web has gotten quite complex. There are no more "webmasters" for moderately complex sites and there are not really even many "web developers" - there are designers, FEDs, devops, backend devs, content strategists, technical SEOs, analysts, content producers, etc. At this point, it's rare to find a good backend dev who is also a good front-end dev unless she started as an FED and transitioned... but even then, within a few years, might be outdated. The skillset has come a long ways from the days when you could write some HTML tables, stuff some keywords in a meta tag, install Apache and call yourself a webmaster, web developer and SEO.