This is incorrect. Perl is still seeing good adoption by new developers.

Now your argument could be that it probably not at same rate compared to some of the top languages around at this moment but Perl is still growing.

Some facts...

- CPAN continues to grow - http://cpants.cpanauthors.org/stats/uploads | http://cpants.cpanauthors.org/stats/authors

- According to this tweet Perl still produces more new repos on Github than languages like Scala, Clojure & Go - https://twitter.com/dberkholz/status/395922559151009792

>was it a design decision or they chose it as no alternate mechanisms/libraries is available in perl

No idea what their decision criteria was however they are plenty of alternative mechanisms/libraries in Perl.

See PSGI/Plack for Perl's state of the art solution - http://plackperl.org