We had to pick something that was "good enough" for compression time/size, as well as easy for our customers to download/view if they wish, on any OS. Zip being supported in every popular operating system, and the average user using Windows being able to right click -> unzip, was the primary reason for choice.

There are of course significantly faster and more efficient compression formats like LZ4 which would be ideal if we were solely using the data internally in managed environments, but we offer these backups as downloads to our users, some of which aren't very technically inclined and still need to be able to access the files easily.