Because I use perl on a large number and variety of machines where installing modules is not always practical or possible, if it is in core I don't have to worry.
I understand there are moves afoot to "slim down" core and I don't object to that but personally I think both of the modules I mentioned are small and useful enough to warrant including them... not that I expect my opinion to carry any weight :)
-- Do not seek to follow in the footsteps of the wise. Seek what they sought. -Basho