Google's fault that SEO exists? The incentive isn't even there, they want people to pay for ads rather than gaming their results. But SEO finds a way.
The people that have money and time to put into SEO are the people with ads on their websites.
I bet a large number of them run Google ads.
As such, it is not in Google's best interests to cut them out of search, regardless of how low quality they are.
It is well known that Google and SEO have a wink wink / nudge nudge relationship where Google "hides" its search algorythm, and somehow the websites with the most ads get closer to the top every year.
They literally control the feedback loop...