How about:

Because I get paid to use Perl5, because I don't have enough time to play around with Perl6 and because it isn't finished yet anyway and I'm pretty sure I wouldn't be able to use it on production systems? :-)

Now don't get me wrong, I think it's a wonderful thing what is happening around Perl6 and I try to follow what is happening, but not all of us have the time to do real work with it.

*wanders off to a meeting saying "darn, I haven't even started on the slides for YAPC::NA..."*