Because attacking is entirely one-sided and there is no capability for the defender to react tempo is literally the only thing that matters in this game. Control decks are just too susceptible to getting slightly behind and never being able to catch up, and since the entire game is predicated on trading your creatures for their creatures efficiently the attacker has a massive fucking advantage. The number of low casting cost cards that can allow you to catch up once you lose board control is negligible. Wrath of God? 8 mana in this game. The only way to efficiently deal with your opponent's creatures is with your own creatures, and once you get behind the person dictating combat has to really fuck up to lose.
The warlock deck which is nothing but tiny shit and removal fueled by the class ability renders the vast majority of decks irrelevant. You can't fix it either because silence nullifies all the creatures that could ostensibly give board control immediately and there are no non-creature mechanics that are fast enough to overcome aggressive decks. The whole game just comes down to getting an attack advantage and pressing it with your class ability.
I've tried to make slow control decks work but there is so little margin for error that a slightly below average draw can often lead to death, or if the other guy draws his "good" hand you just roll over and die. That hunter deck with it's stupid fucking class mechanic is the prime example of that principle.
The only way to fix the game I can think of without adding more card types would be to give every creature in the game an ability to taunt for a flat mana cost each turn. And it would have to be something negligible too, or maybe cost 1 life or something. That or make mass removal much more efficient than it currently is.