Because Apple is trying to get people used to the idea of not worrying about whether an app is actually open or not, since in reality it makes little difference anymore.
I cant imagine why anyone wouldn't want them on, and I can't understand how so many people are excited about being able to turn them off.
I suppose if all you do is browse the web its great. Otherwise, stop trying to decide whats best for me (and getting it wrong), Apple.
I cant imagine why anyone wouldn't want them on, and I can't understand how so many people are excited about being able to turn them off.