The case of the supersized shebang

As a sysadmin who used Perl 4 there were key advantages over shell, otherwise some utilities would have to be C. Perl was much faster than shell by reducing fork and calls to utilities, it gave access to the C library, so could read system DBM files for example directly.

Indeed it re-read the #! line, IIRC to allow perl flags to be set and magic with env as perl at that time wasn't established in /usr/bin/perl.
Perl had extreme portability, it would use some tricks to work on 'broken' systems too.

The later Perl 5 gave more flexibility, but using dynamic libraries made the installation more fragile.