Legal risk from visiting mixed-content adult sites?

Hello all. So in the past I have occasionally visited certain adult websites that host adult manga content. The content I consumed was drawn and was depicting legal adults, i.e. ordinary stuff. However, I recently learned after stumbling upon it that that is not the only kind of content that is depicted, and some of the manga on a particular website (nhentai) also depicts drawn images that may be minors.

This shocked me quite a bit and I reported the content, though worried nothing would be done, so I made a report to the NCMEC cybertipline. I dunno if that's going to do anything.

If the websites host content like that, how are they legal? This website in particular apparently gets tens of millions of visitors a month. I know there's a whole legal grey area, but with some state laws being more strict do law enforcement in those states not go after it?