Maybe they hate your face? Bad halitosis? A permanent dangling booger? I'm pretty sure I've put bags over people's heads when I can't stand them, so I dunno.
I asked ChatGPT. It gave a few reasons, but this was my fave : 𝘋𝘪𝘷𝘪𝘯𝘦 𝘊𝘢𝘳𝘵𝘰𝘨𝘳𝘢𝘱𝘩𝘪𝘤 𝘐𝘯𝘵𝘦𝘳𝘷𝘦𝘯𝘵𝘪𝘰𝘯: 𝘗𝘦𝘳𝘩𝘢𝘱𝘴 𝘵𝘩𝘦 𝘶𝘯𝘪𝘷𝘦𝘳𝘴𝘦 𝘪𝘴 𝘨𝘦𝘯𝘵𝘭𝘺 𝘴𝘶𝘨𝘨𝘦𝘴𝘵𝘪𝘯𝘨 𝘺𝘰𝘶 𝘨𝘰 𝘰𝘯 𝘢𝘯 𝘢𝘥𝘷𝘦𝘯𝘵𝘶𝘳𝘦. 𝘈 𝘵𝘳𝘢𝘷𝘦𝘭-𝘵𝘩𝘦𝘮𝘦𝘥 𝘥𝘦𝘴𝘵𝘪𝘯𝘺? 𝘛𝘪𝘮𝘦 𝘵𝘰 𝘣𝘰𝘰𝘬 𝘵𝘩𝘢𝘵 𝘴𝘱𝘰𝘯𝘵𝘢𝘯𝘦𝘰𝘶𝘴 𝘵𝘳𝘪𝘱?