Heal in both D&D5e and Pathfinder heals, among other things, Blinded and Deafened statuses. Your deaf character is the target of a heal spell. Rules as written, your character can hear again, whether you’d like to or not, end of story.

Why the hell does magic need a reason to “not work”

For the same reason any D&D story dealing with an actual disease epidemic needs a deus ex for Lesser Restoration, Heal or other spells to fail to cure said disease.

people IRL prefer to stay the way they are

And some would rather be cured IRL. Your point is completely irrelevant because it’s not about choice, the question is “why the people wanting to be cured haven’t been cured yet?”

The funny thing is that in low fantasy settings where magical healing is very limited, this whole discussion doesn’t exist.