As you can see, slightly different answer, so make of that what you will.
All is there - nothing to add
I think it is mainly related to absolutely shitty quality of first S9 batches. Many arrived to US DOA, majority requires downclocking to prevent overheating etc
So - let's see
This is a pretty legit reason from them. I don't think they want their datacenters to burn down because "An early batch of S9s overheated and failed".
What I'm worried about instead is their profit after the block halving. I heard that an S7 will never make any profit unless electricity is free.