And don't assume that they're not also using other services and providers as well. How would you provide desktop services and solutions to 80,000 people distributed all over the world?
If you have a solution that doesn't cost $1bn, please write the white paper. I'll gladly write the RFP response and we can enjoy our profits. :D
The numbers may seem staggering, but this is how much shit costs in the government. Most of our competitors in my space are offering services with 2%-4% margins because the government is so stingy about how the work is performed. DISA alone is probably at nearly the scale of AWS in terms of compute power and system requirements. And they probably have 5-10x the number of employees. It's not a trivial problem to solve, and I've been working for contractors for 10+ years now.