Different devices service different audiences. The moblie players are looking for something relatively simple and quick that they can start up on their break or while taking transit to and from a destination. They may not own a computer so their only method of playing the game would be on their phones.
PC players might already have the client on their computer so downloading another game isn’t really a hassle, they love performance and visuals along with easy to use interfaces. They are already using their computer for other functions, they boot up a game of Hearthstone and tab out to browse the internet or do something else in between turns.
I don’t know why you seem to think one method is strictly superior. You also seem to imply that the game runs exactly the same on both devices. It doesn’t.