The fact that gaming companies never open source anything anymore, even their thirty year old shit they don't even TRY to sell anymore, is a travesty. It was never that popular, but look at what cultural cornerstones Doom and Quake managed to become. Being great games helped a lot, but opening them for the community to maintain is what solidified their positions.
Of course, if you're still playing Doom or Quake or Warcraft 1/2/3 or original StarCraft, how much harder is it to convince you to buy the latest rerelease or shitty sequel? Or what if a competitor *gasp* moderately improved their code by studying yours? Fuck the culture, we need to make 0.3% more profit.