It is hard to filter out SEO rubbish with a low rate of false positives. Spammers became really good at pretending to be real sites. For mail spam various trus

It is hard to filter out SEO rubbish with a low rate of false positives. Spammers became really good at pretending to be real sites. For mail spam various trust-based solutions like server black lists, domain verification etc. were important to solve the problem. But Google has little incentives to push for a trust-based search due to their business model.