Metallica ”…And Justice for All” also sold a lot. I can’t think of any band or artist that made it to #6 on Billboard BEFORE they even released any video or promotion in mainstream radio/TV…
Or 17 weeks on ”top 30”. Only a few other albums I saw on the chart in the late 80s stayed on there for 80+ weeks.
I think the only hard rock/metal albums that stayed there longer was Guns n roses - Appetite for destruction and Def Leppard - Hysteria. Maybe just a few more that I missed, but definitly not any ”heavy” metal albums.
Something happened for other thrash metal bands in 1990 though: New aibums from Megadeth, Slayer and Anthrax went higher then ever on the chart.
Even thrash bands like Nuclear Assault made it to ”top 200” in 1990. Personaly I think the success Metallica had in 1988-1990 was a big part of it.
I am not saying that the ”Justice” album sold as much as The Black album, or even close. But, they already sold millions of albums before 1991 as a thrash metal band, I think they had basicly already ”made it” 🤘