In practice the US government is constrained from paying market rates for tech talent. It can either hire companies to complete the entire project, or it can hire a consulting service (which skims off a massive overhead) to provide technical talent inside a government agency.
I would argue that this is obviously a national security operation and the shell company is operated by the FBI or the NSA, not necessarily some random contracting firm.
I read the article but I believe the key point is since when 11.x.x.x stopped being dormant addresses, instead of these IPs just transferred ownership but not “dormant”.
As an interesting fact, when searching “aliyun 11.0.0.0” which is the mentioned Chinese cloud provider I believe, they apparently has been using that as internal IPs since 2015 as well