I don't understand the extreme amount of work that people put into works like this that could be shut down forever at the whim of the copyright holder.

"There is ongoing debate about to what extent fan fiction is permitted under contemporary copyright law. Some argue that fan fiction does not fall under fair use, as it is derivative work. The 2009 ruling by United States District Court permanently prohibiting publication in the United States of a book may be seen as upholding this position." [1]

Unless we can greatly reduce the length of copyright terms and/or clarify that fan fiction is allowed, you might as well create only original works so your months or years of work doesn't go to waste.

Update: From the link another HN user found, it says, "The Bartkira organizers knew that Matt Groening had seen a copy but to date have never received a cease and desist order. As an extra defense, Harvey decided to donate all of the book's profits to charity [including] Save the Children, a charity preferred by the late The Simpsons co-creator Sam Simon."

So the creators are walking on eggshells, making sure they don't earn a cent and hoping the copyright holders don't sue one day.

[1] https://en.wikipedia.org/wiki/Fan_fiction#Legality