Sony has explained its reasons for dropping the 3.5mm headphone jack on its new Xperia XZ2 series. According to the company, it is because of design reasons and the market trend towards wireless headphones.
https://www.notebookcheck.net/Sony-says-it-is-following-market-trends-with-headphone-jack-omission-on-XZ2-Compact.289250.0.html