... and exactly where is the overwhelming business justification to change anything?
In my business, where I am the technical manager, it's very simple. We don't run unsupported versions of Perl. While we may never run into bugs in Perl that could block our business, the fact that we're never getting those bugs fixed in unsupported versions is a bigger risk than that of upgrading frequently.
A blocker bug means we lose real dollars. Testing an upgrade means launching an automated process and, almost always, getting the green light to proceed.
Certainly upgrading regularly has an upgrade tax, but in the case of Perl it's reasonably easy to test upgrades and deploy upgrades, and that tax is much, much less with a good process for upgrading regularly. Perl 5's predictable release and upgrade schedule, as well as the entire CPAN infrastructure, is immensely helpful.