when a character has multiclassed, he gets ability score improvements as per the classes dictate. Wouldn’t it be better for the story/role-playing to have the ability score improvements fixed at certain overall character levels?we really like having the class table serve as your one reference

— Mike Mearls (@mikemearls) December 4, 2017

I always thought it was also tied to class progression to reflect the attributes of the class itself. Example, the fighter is focused on mastery of body and as such gets more asi’s. Yes, it’s part of class progression, which is why it’s on class tables.

— Jeremy Crawford (@JeremyECrawford) February 25, 2018