Don't have a port, and user will be forced to buy the new headphones => profit for the market. Implement some "genuine accessories" program that'd start spamming user with alerts if the connected headphones won't pass Apple-style cryptographic handshake and they'll have buy it from you => profit for yourself. Also allows for vendor-specific proprietary extensions that weren't easy to have with analog plugs (but still existed), but easy to have with USB-C. Oh, and tell users that it's all for them - improved audio quality (in earbuds, yeah), thinner smartphones, and whatever other advantages marketing division could invent - and users'll eventually accept it.