That's just it Foxmoth. People don't brief. They are either assuming, lazy, ignorant or arrogant. Take your pick. Seen them all in action.
Too many examples to cite. Straight in approaches in an active circuit is the worst, followed by overtaking in the circuit. People calling up Sywell asking for join instructions for their Expo. For crying out loud.
Last year, we had someone flying abeam our approach to the same runway via their own straight in approach. Radio call was akin to "joining from the SW"' only followed by "final". Bloomin formation flying !
This, despite a firm overhead join notification from the airfield in question. Butter didn't melt in the mouth when the individual was confronted, neither did the airfield (not Sywell btw) share any concern. Needs a number of collective party activities to eradicate and there in lies the problem.