The point I was meaning to make is that it's quite easy to make a site uncrawlable, and therefore unfindable in search engines.

e.g. Google always had problems indexing Flash websites. It historically had issues with sites heavily relying on Javascript. Nowadays it's less of a problem, at least for Googlebot.

Though a useful side effect of SEO people finding it to be a useful side effect, is that what they are doing for their gain may help overall accessibility (where too often the opposite is the case, when people trying to game systems accidentally affect accessibility, it is usually negatively).