Protect screws in joint and make it look nicer?
Is that a hand rail of some sort? I would not want PT wood on a hand rail, the chemicals used to treat it are dangerous for human skin contact. If it is a hand rail, I would get a better untreated wood that can cover over the entire arrangement, then use a safe stain or sealant on that new wood. Offset the joints so that they don't line up with these joints and you kill two birds with one stone.