There are a few haste spells in the game, SCH and AST have group ones and WHM has a selfish one.

But if you're looking for the classic version, we had this discussion a long time ago. The answer really boils down to; Haste is brokenly powerful. To bring it over to a MMO environment as-is from single-player gameplay would require re-tuning all content around it. And since it would then part of every strategy for every boss ever, would it feel as powerful?