At least we would only get one letter in the mail, and one news story, about the breach rather than the constant trickle of government breaches!
From an operational cost savings, single cloud makes sense. Depending on what metrics are being reviewed, it may even make sense from an anticipated uptime perspective. I also do not have a problem with the 10 year term; it is going to take 11 years (yes, more like 22) just to transition.
The "government" part of a business decision is perplexing. It is public money, and the government is not supposed to pick winners and create losers with that money which something of this magnitude can certainly do. However, if they put a portion of the contract in the hands of IBM or smaller cloud then they are funding way too much of that smaller cloud, thus jeopardizing the way it operates (would become the ibmcloud.gov). Where as larger players (AWS, Azure, Google) likely view the DoD contract as an amazing win, but not funding their future. At the same time, using taxpayer money-- that is going to be spent regardless --to foster competition and innovation by spreading out the contract has its own merits.
Tough call. I am interested in reading the documents should they ever be published for public review.