Those shitty SEO spam sites exist only to serve ads, and Google has a monopoly on internet ads. So there is no real incentive for them to solve the problem.
Google has 28.9% share, Facebook 25.2%, and Amazon has 10% and growing fast. Not a monopoly, and the incentive is there: if search results are consistently bad, people will stop searching as much, and revenue and market share decline.
Google had the same incentives in 2011, 2012 when they built and released Panda and Penguin.
Real review sites serve ads too. I don't think Google has any incentive to make things worse, and they still want people to google reviews instead of just asking friends or people on reddit for reviews.