Because originally tar only dealt with tape archives. So the default behavior was (and still is [EDIT: correction, apparently a lot of GNU tar distributions hav

Because originally tar only dealt with tape archives. So the default behavior was (and still is [EDIT: correction, apparently a lot of GNU tar distributions have defaulted to using -f- which sends things to stdout. That is not how tar originally functioned]) to send the results to /dev/st tar was later changed to read/extract(-x) and write/create(-c) from files(-f). And was also modified to handle gzip(-z) and bzip2(-j) compression. Essentially, the problem comes down to having to support all of the old scripts that depend on default tar behavior, even though people rarely write to tape drives with it any more.