Why do people act like Boxers under 220 lb are not heavyweights ?

Probably because they made weight divisions and label what used to be HW as less than HW. It's sort of like the lineal champ jargon. You can preach what was or should be until the cows fly but given the structure and verbiage of the sport and those in control of it; it's a quixotic endeavor for sure.