Log4j 1.x was indeed ubiquitous at one time. SLF4J took most of the mindshare before Log4j 2.x got traction and Log4j 2.x is not the go-to Java logging solution today. Spring, for instance, defaults to SLF4J. Huge code bases that were heavily invested in Log4j 1.x often migrated from 1 to 2 due to API compatibility and these account for most Log4j 2.x usage today. That's the history as I see it.
Had most developers not done Log4j 1.x -> SLF4J and instead waited for Log4j 2.x this problem would be much worse than it is; a vast number of small, neglected services would have had to be fixed. The thought that I'm having is now that the power of compromising these logging frameworks has been demonstrated the ransomware crews are going to look very hard at them and find more large holes.