...Because law enforcement does not have the interest, reach, or time to investigate every single cybercrime, and if they do it won't be timely - it will be after the fact, punishing the criminals, and not preventing harm.

Google is in a unique situation to protect their users, and they also want to avoid serving search results that are malicious (yes, I know about their ads problem) - so they are proactive about scanning for sites that are malicious so they can avoid sending users to them.