I am sorry I didn't mean to imply that it was automatic. But at least you should wait so you can make an informed choice.
"Better part of valor" and all that.
Yes it's technically optional, but realistically everyone will end up using it because no one wants to have subpar gear. If you want to have the top of the line gear in order to satisfy people in your raid group then you will have to reset your gear.
So Op has a valid point, which is why bother upgrading your exotic gear when you are just going to reset it eventually anyways.