If it is justified, why shouldn't dictionary definitions change based on legal changes?

It depends on the word and how many people refuse to accept the change, as to why it is not wanted to be legally changed. Personally, I feel if the legal definition does not match the current dictionary definition, the dictionary should change.I care not if it refers to marriage, sexuality, living beings, what have you. The fact it changed legally to me signifies that the majority has come to terms with the need for change, so the minority needs to stop complaining and let the change happen.