Cone-shaped AoEs tend to require a target, whereas 360 degree PBAoEs don't. I wonder if this is due to the fact that the game supports multiple different control schemes, some of which rely more on auto-facing to target than others?

They could offer some UI options around this: e.g. allow AoEs without target - yes/no; allow AoEs to fire at dead target's last location - yes/no. (Suspect that latter may not be easy to realise if the combat engine deletes relevant data as soon as the mob dies.)