Probably because classic European pirates don't exist in the For Honor world. The classic European pirate was birthed from privateers hired by the British, but when the jobs went away these privateers turned to piracy and then pirates lik Blackbeard were birthed. The British empire doesn't, and never has existed in the For Honor world. In the For Honor world the British never went beyond Anglo-Saxons, as the cataclysm stopped them from progressing, then the thousand year war prevented any non-war related advancements. What we see of the knight faction is the British people. So due to their own lore classic pirates cannot exist.

However the Chinese, hardly anything is known about them in the For Honor world. And in the real world there were Chinese pirates, and since the Wu Lin in lore already have gunpowder they can give them a gun, therefore the Chinese depiction of a pirate is more possible in the For Honor world.