Quite a few people have left that were generally cool and nice. (Incognito/Galen The Wise etc.)
Although I can't speak for the ones that come back within the following week. You do have those that no longer post in the forums but still play DOA I believe.
Some people may drop the game due to other fighting games that are coming out,like SF5 or Tekken 7(we all know it's inevitable),causing the hype for Doa to die.I too went forth between almost every fighting game,but once I played Doa 5,I knew that Doa's my fav. fighting game.