Even the biggest ones can come crashing down fast. As a Finn I still remember what happened to Nokia.
Steam has an advantage of already having a captive audience with massive game collections, profiles, achievements, play times, contacts, etc.
So, that audience has a vested interest in keeping buying on Steam. Like, there are people who have over 1000 games.
Though I wonder what will happen if Developers will start leaving Steam en masse.
People shouldn't ask themselves why schools get shoot up.
They should ask themselves why people who finish schools burned out due to mobbing aren't receiving high enough compensations to not seek vengeance.