not sure i understand, the reason square coins have never been common is bc of a siege? why? it looks special
Ah, I apologize for the poor explanation. Square coins have never been common - period. Round coins take a bit more effort to make but are easier to use, so throughout most of history mintmakers have preferred making round ones, with some exceptions. The siege was the reason for why Groningen in particular made square coins - they could not access the expertise of the mint and thus made coins in the most basic way.
I changed my original post to make this clearer.