*** Because He’s God.*** Well, duh. What about Philip? One moment he was with the ethiopian on the way to Gaza and the next moment he was found at Azotus (Acts 8:39-40).
Just because angels are created beings does not mean that they don’t have a different reality, because they do. You said yourself that they are sent to earth. So Guardian Angels are sent from heaven to earth to protect us. I don’t see anything contradictory about an angel being in heaven while we are sleeping or doing things that don’t need their protection and being with us when we need them.
So “always” doesn’t really mean always?