Logic Behind Nerfing Udyr and Not Broken Yi?

Nobody plays yi. I have seen more urgots than yis over the last 30-40 games. But when I see him he has usually no impact on the game.

Maybe because can't build tanky and stun you every 3-5 seconds while still dealing tons of damage. Though he is fast, he doesn't get a speed boost every 3 seconds by spamming bear stance and stunning all who try to kill him.