1) The large amount of spam comments we see are not necessarily the reason for a website's ranking. To reduce false positives, search engines usually ignore spam comments instead of directly punishing websites with spam comments, as doing so would be too dangerous and easily exploited to harm competing websites. The rankings of these websites are likely due to reasons we haven't discovered, such as having some very strong external links.
2) Not punishing now doesn't necessarily mean there won't be punishment in the future. Saying "punishment" isn't entirely accurate; more precisely, when search engines detect these spam comments, they remove the weight and voting power of these spam links, causing the website's ranking to drop. This might appear as punishment, but it's actually just bringing the website's ranking back to where it should be.
How do search engines determine spam comments? There could be several methods:
- Look at the time relationship of the comments. For example, if the same blog has a comment link from the same website appearing on different posts within seconds, this is definitely abnormal. Or, if a website's spam links appear on multiple blogs almost simultaneously. Individual bloggers may not notice this, but for search engines, detecting these patterns is effortless.
- Does the comment contain a URL? Is the URL just plain text or made into a hyperlink? Some spam comment software or spammers have greater ambitions, leaving URLs not only in their signatures but also within the content of their comments. Among filtered spam comments, I often see pages and pages of junk. I estimate that even the dumbest search engine could identify such spam comments.