Sure, they could possibly make a deliberately terrible autocast, but that's not what people want, is it. They want a great autocast that is smart and fast.
This.
People moan for an autocast, if one is implemented in the game and it doesn't live up to people's expectations of an easy "I win" solution, it'll do more harm than good.
Those RTS games I've played which supported autocast has only been for very specific abilities (like priest heal or sorceress slow in wc3) because the other abilities are far too situational to be used as an autocast and a healthy amount of skill should be required of the player.
