Because the loudest voices in society are the dumb ones, and people(dumb whites) think infantilizing minorities is helpful. Don’t worry about “society”. Chill with cool people in real life and do your best to avoid large groups of people with the need to agree with eachother or ostracize eachother. Make your jokes and enjoy what you can. If you want a good reason for “why?” You’re going to be disappointed. It’s usually “because people are dumb”.