Because the remote control applications found on Phones and tablets are generally harder and more clunky to use, even when designed for your specific media player.
Because it’s easier than setting up a separate Infrared receiver on your Media Player and works just as well.
Because it is the simplest and most effective way to control your media player.
Any Media Player or Media Device that uses HDMI-CEC such as Plex, XBMC, Kodi, Chromecast.
This how to guide discusses how to get your TV remote working with your Media Player using HDMI-CEC.