@hawkeye10,
So..? Do you think they didn't make an impact here? American music industry in the late '70s and early-'80s there was such a diverse selection of musical groups and a broader spectrum of types of music that sold records ... with a lot more discretionary cash than in Europe. Also record promotion differs here than in EU or UK.
It would seem as though having a Broadway play (Mama Mia) about them sure seems to indicate they're far more popular than their initial record sales indicated. They so grew in popularity to a great degree over the years- way beyond the popularity of disco music trend.
Back to the subject, what do I think of Abba? I own zero of their LPs, or CDs. However, I can sing almost all the lyrics to every one of their hits and I play them on Youtube fairly often. I like them,,,but it was because they grew on me. I still like cotton candy too. After all, it's happy music and fun to move and dance to.