How do we know that Charles hasn’t apologised to his sons, possibly more than once. Sometimes apologies go ignored, or don’t fill the need, and the apology needs to be repeated again and again, but is never enough.
How would we know the apology status in this particular family, or any family, it’s private. Harry has made his need public, but we don’t have the full picture (and it’s not our business, we didn’t ask for it).
However, he’s put it out there for public consumption and debate so, understandably, it’s being talked about.