Why does a Olaf with no damage items do more damage than a Vi with damage items?

I think this is the stupidest thing ever because first of all no one likes the tank meta, yet Riot decides to keep bringing it back in. In a game I recently played an Olaf built straight tank yet he did more damage than everyone on our team. This is the most retarded thing I have ever seen. Can someone answer why Riot likes the tank meta?