Why are antis so obsessed either age gaps?

Age gaps always seem like the first thing they latch onto when trying to shame a ship. It’s always “but that character’s a minor???” or “Character A literally knew Character B as a child???” or even just thinking the age difference is too much even if it’s legal. It’s the strangest case of tunnel vision too because a lot of the times the characters themselves have probably done more questionable things, Hannigram is a popular example that comes to mind. Do they even realize how infantilizing it sounds especially for characters that are grown adults? This isn’t even an issue strictly for antis but the masses as a whole have always seem to hyperfixate on age gap relationships to the point creators feel the need to explain or justify writing about them which seems so unnecessary.