As an example, the bits of Google's original algorithms that they did talk about (pagerank using reputation of in-links to propagate to a page) publicly began g

As an example, the bits of Google's original algorithms that they did talk about (pagerank using reputation of in-links to propagate to a page) publicly began getting gamed into irrelevance fairly early on (link-for-link schemes being the start of the SEO industry). After that it's been a continuing struggle of a whole industry looking for weaknesses and Google adapting. Another way of thinking about it, is that if someone could see what features were most important for the ranking on some site, then they could start to optimize for those, breaking the usefulness of that feature. One obvious example of this is "Please remember to like, comment, and subscribe" on YouTube.