Okay I vaguely remember that new Canon of Boba Fett ≠ Mandalorian, thanks RogueLeader.
And yes I can get behind those explanations. I kept wondering why would the Empire be so antagonistic against Mandalorians. Then I recall that, and although not all parts of the KOTOR era are canon, the Mandalorians did spearhead a campaign against the old Republic with devastating consequences. So in my mind, the Empire couldn’t risk any internal or external influence that could have sparked the Mandalorians’ interest in starting another war.