Why would living on Coruscant or Alderaan necessitate people knowing about the force as a fact? I mean to most it's just a religious concept, like many many others that are shared by many many religions.
Even during the height of the Republic when the Jedi were at their peak, to most citizens of the capital, if they heard about them at all they were either some weird, shady religious cult of sorcerers and soothsayers that advice the politicians, and on the odd occasion one does venture down to 1313 or thereabouts, it usually results in trouble and/or dismemberments. If anything, they'd be a ghost story to most ordinary people.
As for Alderaan: do the Jedi have a temple on Alderaan? Or any significant presence at all? How often would any Jedi have cause to go to such a peaceful world? And in the time of the Empire one imagines it's flat out illegal for the universities to teach anything Jedi related, or indeed anything at all that doesn't line up with the state sanctioned curriculum. Again, anyone that's old enough to know different knows to keep their mouths shut, while the younger generation just aren't going to be told any different.
Here's a real world example of how fast and pervasive information suppression can be: until the new 'Watchmen' TV show I had never heard of the 1921 Black Wall Street Massacre, a reaction that seems to be shared by most non-African American viewers. It's by no means a secret, but it's simply not taught which is astonishing given the facts of the incident and many many many similar ones across the 19th & 20th century. If what I read is correct: the generation born in Tulsa after the massacre (black and white) were just as ignorant because *nobody talked about it*. Not the survivors, not the perpetrators, not the press and certainly not the government. It took *decades* for it to come to light.
Or the intent is to show that after the Mandalorian Purge by the Empire, many of the surviving Mandalorians chose to incorporate a new tradition (perhaps based on an old one that fell out of favor with many factions because of its rigidity) of not removing their helmets in front of another living being. In addition to becoming a quasi-religious function, it would help to conceal their identities and keep their families safe(r), something that would be of great concern after the Purge with so few survivors left.
My money is on this being a super orthodox cult that was once the spiritual arm of Death Watch, which after the schism caused by Maul and subsequent purges by Bo Katan, and later by the Empire, it became all that was left of that organisation.
If they follow the pattern of such groups then they probably consider themselves the only "true" Mandalorians because they follow The Creed and that's all that counts.
I don't think Vizla was ever a true believer; he just wanted power for himself. Those that followed him like Clan Wren seemed more moderate and mostly concerned with loosing their cultural heritage (and possibly the prestige and influence that it afforded them) to Satine's pacifist reforms. And again, to them it's not a religion, it's just culture and heritage. That whole "never take your helmet off" is just some archaic nonsense from eons ago and about as relevant as tales of mythosaurs riders and the Jedi Crusades. The kind of thing only fringe zealots buy into.
I'm still not 100% sure what Bo Katan's deal was or why she fell in with Vizla; we've seen her complicit in what can only be described as terrorism, not just the bombings against political targets, but enslaving and murdering powerless villagers simply because they can. I'd really like to see her and Satine's backstory explored at some point.