If someone legally changes their name, that would indicate to me that the subject wishes to be known by the new name. Yet Wikipedia will still list the birth name.
People change their names all the time when they get married or immigrate and have no problem with their birth name's being available. I don't think it's fair to make a blanket statement about this.
And some trans people "have no problem with their birth name being available," even if they have stopped using it. "Blanket statement," and all that...