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.
And S7 is just a year old and yet will no longer be profitable due to less mining rewards, difficulty increase and expensive price (especially the first few batches). Anyone holding S7 must start selling and go up to newer miners to avoid being left out.