As the title says I'm curious about whether there were ever any unofficial mods or maps (I specifically mean fan-created) for Doom/Heretic/Hexen that needed to be paid for.
So far I have not encountered anything like that. I have some guessed explanations for that. Please comment on these and enlighten me

1) It is illegal. I think I remember something about the Doom license disallowing taking money for any fan-created mods and levels. Is this true? Would this also be true now that the Doom engine games were released under the GPL?
2) The Doom community doesn't like it. Because so many mods and maps get released every month for free people might call the ones wanting money greedy.
3) Similar to 2): Because so much free stuff gets released no one would pay any money for something like this.
4) No one wants to try selling something for a game that's 20+ years old. The expected profit would be very low because the whole community is rather small compared to newer games (even though Doom has quite a large fanbase).
I'm coming up with all this because the thought crossed my mind that if people could take money for their mods maybe even more mods would be released or they would have higher quality because people could spend more time on them (because they would earn money doing this).
I could even imagine that for myself. Creating mods and coding for them (doing what I like) and earn money at the same time. Obviously I personally would not expect to make some big profit. However I think this would be cool, not only for myself but also other people enjoying creating new stuff for games

Please share your opinion on this. Also I would like to hear if there is anyone among you who would pay some small amount (like 5-10$) to play a new mod or set of levels (price depending on mod/map size of course).
Thanks for your time, I hope to see some interesting discussion about this
