One reason that stands out, is the sunken cost fallacy in regards to the amount of time and money people spent on game (namely online ones, given that if the servers go down, the game is unplayable for the most part, private servers aside), because the said game is a very niche one (DOTA 2 fans come to mind, because of the superiority complex that some people have, that DOTA is the ONLY game they play), or because a game is virtually the ONLY game title in it's genre. (The Sims series comes to mind, and former TS4 Dev Grant Rodiek said something along the lines of this, saying that "There won't be a Sims 5, if Sims 4 fails", as a response to TS4 being extremely barebones on launch.)
The increasing pushes to make games into Live Services, with planned obsolescence, does not help matters either.