I was a 15 to 18 year old in the mid-‘70’s, so I understand why many people mistakenly think ABBA dominated US airwaves when actually, they didn’t as they only scored 1 #1 hit here. The primary reasons for that were:

1. The band focused too heavily on the European audience as it was their "Backyard" so-to-speak and didn't require much effort to reach given they lived there and were primarily an 8 to 10 member highly engineered Studio band, not a performance band.

2A. In the mid to late '70s, for a band really to conquer the US, they were expected to tour as live concerts created additional buzz / attention with both new / existing fans and the local media in the towns played. Additionally, here in the US, live concerts were a powerful driving force behind album sales. Whether as the Headliner or an Opener for other bands, groups of the time, for example: Aerosmith, Boston, REO, Styx, The Who, Rolling Stones, RUSH, KISS and etc toured heavily to connect with fans, promote their albums, drive sales, get even more radio airplay and in turn, stay relevant. ABBA didn't value touring though and instead remained primarily a European studio band with easy reach to the Euro market.

2B. ABBA, by miscalculating the touring work necessary to take on music's most significant and largest market (the USA) and by being stubbornly unwilling to be an Opening Act for other bands in it, meant the group would continue to stay primarily a European based Studio Band. Even in Europe, the band remained timid resulting in only about 250k people seeing them on the first tour in 1977.

3A. During the last half of the '70s, the songs released by ABBA fit better into the "Dance Band" and Disco categories rather than their previously established mainstream Pop genre. But, in 1978 with Disco and Dance oriented music's popularity fading fast and New Age bands like The Cars, Blondie and The Knack commanding attention, ABBA lost even more traction with mainstream audiences.

3B. By the time ABBA came to the USA in 1979 for a six month tour, the band's relevance and popularity were in steep decline. The six month toured consisted of just 15 shows, not near enough to hold onto their fans given the evolving music scene at hand. Since other popular bands of the time typically did 2 to 3 concerts each week, a typical music fan was more likely to see them than catch an ABBA show. As the saying goes, it was too little, too late and ABBA headed back home to Europe again without ever capitalizing on the North American market.

4A. As 1980 drew close, by staying a Euro band and sticking with their traditional sugary based, soft sounds and dance themed music style and combined with their unwillingness to properly tour, ABBA's time in the spotlight was practically over. Like many of the Soft Rock bands of the '70s, the rise and phenomenal popularity of louder, harder-n-faster, guitar driven, Glam, Hair and Metal bands such as: Poison, Van Halen, Def Leppard, Cheap Trick and AC/DC took control and dominated the music scene in terms of widespread appeal, radio airplay, fans, sales, concert tickets, merch and overall revenues.

4B. Those bands were fueled by their dedicated fans through constant touring and powered like a rocket by MTV. In reality, these bands slammed the door shut for good on the '70s era of ABBA oriented, Soft Rock, Dance and Disco music. By 1981, ABBA was on life support and the following year, 1982, ABBA broke up, disbanded completely and began a slow fade as they coasted then aged out of contemporary musical relevance. Of particular note is the fact that many of the Glam, Hair, Metal and Hard Rock bands that replaced ABBA are still on the radio, have huge fan bases spanning decades, and continue to tour 40 years later here in 2023.