I think there are so many different factions for the Mandalorian. Jin was a part of a certain faction and Bo Katan was a part of a different one, she seemed to have no problem removing her helmet and didn't have the strict honor code.
It goes back to The Clone Wars, as well as Rebels (really, really abbreviated version):
Death Watch were hardliners, preferring to stick to the old traditions of when the Mandalorians were purely warriors. They were essentially labelled a terrorist group by the Mandalorian government and were pretty small after the Mandalorian Civil War.
But, they were based on Concordia (Mandalore's moon) - so, during the Night of a Thousand Tears, they were largely spared. And because they had a belief that Bo-Katan and the Mandalorian people were cursed because she was given the Darksaber instead of earning it, they felt validated in their beliefs and became even more zealous in them - and this is the faction that Din Djarin is (was) a part of.
Bo Katan was Death Watch, but left when Maul took over prior to the end of the Clone Wars.
There are undoubtedly some other pockets of survivors floating around, but throughout the various shows there has pretty much been Death Watch, and the "main" Mandalorians - that seems to still mostly be the case.