Why won't Xperia XZs get Android Pie?

We aim to support all premium range devices with the latest Android OS updates for two years after the device has launched. However, we do not roll out software to a device if the platform components of a device do not fully support it, since the device could get technical issues and become slower. Therefore, from a quality point of view, we decided to keep Xperia XZs on Android Oreo.