Another great post and I'm wondering if the airplay was higher than sales due more to pop rock radio needed pop rock vs. what people actually wanted to spend money on - especially legacy Van Halen fans. The Van Hager era lost many legacy Van Halen fans I'm sure and I doubt that loss was able to be made up with new Van Hager fans that really only liked that version and actually bought albums.
For example, I'm an album guy. When I'm driving to my cabin or on a road trip I typically listen to albums (mostly start to finish). Thursday night I was sitting by my bon fire eating grilled shrimp and literally started with 1984 and worked backward for a change one album at at time until I went to bed. I think a lot of legacy DLR Van Halen fans were album fans too. And honestly, in the late 80's there was not a lot of rock albums to buy and Van Halen was new and fresh. Also, 8 track and cassette tapes made transporting and listening to albums much more plausible.
Pop rock radio is more about what is on the radio. People that listed to the radio a lot - may or may not be buying albums. I think the 80s may have also been a transition decade in general for what I'm trying to describe.
Lastly, I liked OU812 a fair bit. Like 3 or 4 songs off 5150. 3 or 4 songs off of FUCK. Have not spent much time on VHIII
@romanianreaper , so I will have to give it an honest listen. Balance had one good song IMO - Amsterdam. I do like the guitar crunch on 'Don't tell me what love can do' - or whatever.
tl;dr - I'm pontificating on why early Van Halen sold more albums.