It is probably too expensive (development wise) to scale for this many concurrent users as it will only happen once (or twice in case of expansions) during the whole lifetime of the game.
That's expensive.
Compared to that servers are cheap.
WoW also had launch issues. Players complained. Money hats were made.
But yes, if anyone realistically thinks these server issues significantly alter sales, they must have also forgotten the SC2, WoW, DiabloII launch.