I could easily see adding the Rolling Stones and Elton John, but the BeeGees and Abba were very specific and focused groups with much less yearly distribution than the others. In America, we might know those names, but Chinese listeners, Hindi enthusiasts, even in Africa, they all know Elvis, they all know Michael and they all know the Beatles. I am not sure about the Rolling Stones and Elton John. I think they would recognize many of the songs and tunes, but not necessarily know the artist. They KNOW the others.
The Bee Gees had two advantages over the other two. The songwriting catalog of the Gibb Brothers exceeded that of the other two acts. In addition, the Bee Gees were a solid, well-known band before they reinvented themselves in the disco mode and shot to the top of the music world. This evidences more versatility and longevity than the other two.
At the height of the Saturday Night Fever craze, the Bee Gees would have been at least as recognizable world-wide as Michael Jackson. Of course, that has faded now but then so have the Beatles, to some degree.
Go to Japan or South Korea and look at what they have in karaoke places. Then reassess how far the reach of Abba was - both in terms of geography and longevity.
ABBA was hugely popular worldwide. Nelson Mandela said they were his favorite group.