Because they get more tender and the marbling gets more evenly cooked than you will get any other way. So that well marbled, thick ass steak? Yeah, its gonna be most consistently and evenly cooked with this method.
obviously you can grill a ribeye better than that...
Also, when its done, the buffer time from done to over done is about two hours. So you can have steaks ready at 5:00pm. Your guests show up a little late, you shoot the shit, drink a beer, set the table, pull the steaks out at 6:15pm and they are just the same as they were at 5:00pm. And you did all your prep ahead of time with minimal effort.
Long time, minimal effort.