Also, I think investors forced him out by saying they will finance next round only if Kalanick is gone. And they need more investment, because losing $2bn a year makes them run out of cash soon and inevitably.
Still - Kalanick and his co-founder friends have a control over a board, so theoretically Kalanick can get his ass back as CEO as soon as he wants. If he wants...
The Kalanick-VCs deal might have another background. To cut those $2bn annual losses, Uber needs to change financially. Those changes will hit customers (prices will increase) and drivers (their pay and benefits decrease). So Uber needs an interim manager to introduce them - a "bad guy", who can take the "blame" for it. A change, that will not hit Kalanick's reputation.
But it's all good. Uber will continue to grow. The service is just too good.