The implementation is open source and not owned by a for-profit company that could decide to kill it off in the future.

This is a good thing, because it means that we don't have to worry about a program running on one implementation vs another.

Also, one of the things that Perl is great for (unlike many other scripting languages) is backwards compatibility. A program written in the 1990s for Perl 5.004 will probably run with minimal modifications on Perl v5.36.