

Round coins are less likely to damage coin purses and pockets. No more complicated than that.
Then as technology has moved on, it has proven advantageous for coins to have constant radius so that coin-accepting machines don’t jam on an unfortunate rotation of points.
This is why even when coins aren’t round - thinking specifically of the British 50 pence and 20 pence coins, but there are others - they still have curved sides.



When your neighbour is a bear, it is wise to be wary of it.