John Mueller explained the website which contains adult content are ineligible to serve good results. It does not depend on the amount of content, as Google doesn’t serve good results for adult content.
I think in our rich results guidelines we say none of [the rich result types] are useful for adult websites. But I haven’t checked recently.
I don’t know if anything has changed there but, at least as far as I know, the types of rich results that I’m aware of are explicitly not meant for adult content websites.
SafeSearch Filters By Google
Mueller said the content has to pass SafeSearch Filter to get eligible for rich results. If content fails to pass the filter cannot be considered as rich results. Google loves to be on the safe side by filtering the content of the domain.
With a lot of the safe search filters we try to apply them to a broader URL pattern on a website. So if we see that a whole domain is adult content for the most part, and you have some small part that is not adult, then probably we would filter the whole domain. We want to stay on the safe side there.
If you have individual subdomains, where some are adult and some of them are not, that makes it a little bit easier. If you have separate domains then obviously that makes it a lot easier for us to understand that these are completely separate websites that should be treated differently.
Mueller explained that if a non-adult website has a particular content section for an adult audience, its content will be filtered under SafeSearch Filter. The other way is, some sites have a classified section of adult content, and sometimes hard to separate, then it is hard to figure out how much the site should be filtered.