Shell scripts were too ugly; a maze of pipelines, without anything to debug when the whole house of cards came tumbling down.

Perl was an imperative language like C, except garbage collected, and with many features for writing shell scripts ( sed compatiblity mode, awk compatibility mode), but more powerful than the various shell tools it replaced.

In other words, because it wasn't C, wasn't shell scripts, and Python and the other, cleaner languages hadn't been invented yet...