Imagine that for four years you have been writing fanfictions based off of the harry potter novels.
Imagine, now, that you suddenly decide you will start charging money for said fanfiction.
Let's now imagine that, to read fanfictions, you need a copy of the harry potter novel, as well as other fanfictions that act as framework.
This is why charging for mods is stupid. Mod makers arguing "I need to pay the bills" are loving stupid, so are all the people going "well I should be payed for my work." If you want to be payed, make your own stuff, not mods.