Not to jump on, but there were definitely single CDs - the singles charts (Top 40) were compiled from the sale of CD Singles (and Cassingles, as the cassette versions were called). A #1 hit was determined by who sold the most CD singles, not albums - which is why pop music dominated the Top 10 singles charts, but rock bands would dominate the Top 10 albums. In Australia, a CD single cost $5 up to $10, while an album cost $30.

Also, CD singles were collectors items, because they would often come with bonus tracks that weren't available on the album or anywhere else. Sometimes they were just live recordings, but sometimes they were fully produced studio recordings that didn't quite make the cut for the album, but were still amazing. (Nirvana's "Even In His Youth" jumps to mind, as well as The Prodigy & Tom Morello collaboration "No Man Army".) I still remember my local 2nd-hand CD shop selling a rare Nirvana CD single for $100, and as a kid wishing I could afford to buy it.

That's not quite true: https://en.wikipedia.org/wiki/CD_single

But they were never very popular.

interesting. learn something new everyday.