Comment by ta0o0o0

I seem to recall a profile of the game and it's creators that said it's mostly by choice.

Found it: they were offered 300K just to license the name.

  He has refused a programming job at a major developer 
  (he asked that I keep its name off the record) and 
  turned down a $300,000 offer from another company to 
  license the Dwarf Fortress name, fearing that the 
  proposed sum wouldn’t sufficiently offset the long-term 
  donations drop that would likely result.

http://www.nytimes.com/2011/07/24/magazine/the-brilliance-of...