Websites That Forbid Other Websites From Linking to Them – Pixel Envy:
Some of these are even more bizarre than a blanket link ban, like Which? limiting people to a maximum of ten links to their site per webpage. Why would anyone want to prevent links?
I can actually answer this one: it’s an attempt (albeit pointless) to prevent sites linking in a way which Google will define as spammy. Low-quality backlinks used to be a bit of an SEO nightmare, and you used to have to disavow them as toxic in Google Search Console. More than ten links to the same site from a single page is classic link spam, hence Which?’s attempt to stop it.
