[noirscape]

Is that by any chance related to how the TAR format was developed?

Considering the big thing with TAR is that you can also concatenate it together (the format is quite literally just file header + content ad infinitum; it was designed for tape storage - it's also the best concatenation format if you need to send an absolute truckloads of files to a different computer/drive since the tar utility doesn't need to index anything beforehand), making gzip also capable of doing the same logic but with compression seems like a logical followthrough.

[Suppafly]

I assume tar came first just for grouping things together and then compression came out and they were combined together. That's why the unix tarballs were always tar.gz prior to gz having the ability to do both things.