What have games like The Sims, Civilization, StarCraft, and CounterStrike in common, what Disney Infinity, Marvel Heroes, and – unfortunately – Oni have not?
They are massively popular.
Popularity is what keeping them alive and supported, and what drives the still existing sales of these in part decades old games. Not a massive number of expansions, not DLC, and certainly not microtransactions.
On the other hand, microtransaction and DLC haven't saved a single game that wasn't popular "enough" (which seems to be mostly depending on the distributors expectations).
In addition, I would like to point out that this whole argument of "it's expensive to keep the servers running, so we urgently need a constant revenue stream" only exists because the large distributors happily took up that "games as services" mantra (MMOs and related games aside). Why do single player games like Assassin's Creed or Deus Ex need an online component that has to be supported by microtransactions? You could even ask whether multiplayer games like Rainbow Six Siege really have to be tied to proprietary online services. Was Star Wars Colon Battlefront II from 2005 really a bad game because it didn't have unlockables and some tacked on player progression? With some minor effort, that game is still playable today. Do you think any amount of DLC or microtransactions will save Star Wars Without a Colon Battlefront II from 2017, when (not if) EA decides to pull its plug at some point?