We don't know how long that's going to last. Google didn't charge for control plane either, until recently. So Azure couldn't charge, in order to be competitive. Now that Google has started charging Azure may start too.

Azure also doesn't have an SLA, so that's why they don't charge.

Google started charging after they added an SLA.

Makes sense, the point of an SLA is that you agree to pay back the customer's money if you don't meet it. What does it mean to have an SLA for a free product?