[gpcz]

In this pizza recipe metaphor, are the recipes or the pizzas supposed to be the analogue to software?

If recipes, then the metaphor makes no sense. You can use the "recipe" that is LibreOffice to produce "pizza" that is work products that people would pay for (such as a lawyer drafting contracts, a consultant making spreadsheets, etc). Nothing in the GPL stops someone from profiting from the output of a GPL'd program.

If pizza, then I can only assume the "recipes" would be programs that produce programs, such as compilers or parser-generators. In that case the metaphor also falls apart, since GNU programs of that type have license exceptions that make the output of those programs (and the additional compilation files needed to run like libc and bison include files) usable without following the GPL.