Because queues put load on the servers also. This error you're getting is intentional. Think of the servers like a water balloon. When you fill the balloon up with water, you don't put the tap on full stream, you keep it slow and steady until you get to the point where you think the balloon can't handle anymore water... They're just going to slowly open up the servers to more people, they just can't do it all at once. Server load basics right there.
