That’s kinda the SEO equivalent of security by obscurity though, right? SEO spam puts a lot less effort into optimizing for other search engines, whereas Google is dealing with being the primary target of every adversarial SEO spam site.
This is a great theory but it isn't the reason. Google management made a conscious decision about five years ago to prioritise profit over search quality.
We know this because the emails came out in discovery for one of the antitrust suits.
