Since Android 6, Google have been pushing for the Chromecast devices.
Therefore in order for you to be able to use the Cast feature on the phones you will have to purchase Chrome cast.
You can still stream content (media) to your TV by using Direct Wi-Fi, if your TV supports it, or use a dedicated app from Samsung to control your TV and stream.
... and if HMD were remotely interested in customer satisfaction and producing fully featured devices they would reinstate Miracast functionality
Installing such functionality would make the OS fragmented and not pure. And I like my device to be with a clean Android version.