All the coins issued from Newark are struck upon lozenge-shaped flans, which flans were apparently cut directly from the dishes, trenchers, and other varieties of silver plate, in the town
So yeah, ease of manufacture. Plus that cutting circular blanks would have left the space between as either waste or material that would need to be reprocessed.
https://en.wikipedia.org/wiki/Siege_money_(Newark)
So yeah, ease of manufacture. Plus that cutting circular blanks would have left the space between as either waste or material that would need to be reprocessed.