Lock in is the only concern, but from my experience doing an IDIQ or multi-vendor won't solve the lock in problem. The best thing to solve that is to make sure your using bland normal things not customer government thigs.
https://www.opm.gov/policy-data-oversight/pay-leave/salaries...
Now, think of the political climate: there’ve been decades trying to “trim waste” by steering money to the private sector, where efficiency is taken as a matter of faith. First you’d need to hire the technical leadership to properly plan something like that and then hire all of the people who’d build it, not to mention procuring all of the hardware & data centers, etc. You’re looking at years before you have a positive return on any of that – and all the while, every big contractor is going to have their lobbyists talking about how it’s a waste of money compared to going with them.
NASA tried this a decade ago with Nebula, which was part of the early OpenStack history. I don’t know exactly what happened with that but the people I know working on NASA projects are all using AWS.
Inability to pay high enough salaries for anyone to maintain it properly AND move it forward with new tech.
The history of IDIQ processes is likely a large part of the reason people were anxious to do something different in this instance. Now that it's all politics, it'll probably cost more and function less when all is said and done.
Some aspects of the military, I don't really miss.
Winner take all is also important, because it eliminates the room for sales bullshit. The magic is figuring out how to break up the lots of services so that it makes sense. You don’t want to give any one of AWS, Google and Microsoft everything, so you want to design lots that keep it competitive. This also ensures that any one vendor doesn’t subsidize strategic SKUs by discounting something that isn’t meaningful.
Everything fed is more complex, but it’s all doable.
I doubt their actual justification will ever be public, but I suspect their motivation is that they require a common IaaS platform such that they can have a unified toolset and a single, comprehensive approach to infrastructure security.
Keep in mind also that fewer proprietary features at AWS are available when considering standardizing across all classification types. “East/west” and GovCloud don’t have feature parity.
Having to compete for each task order is thought to reduce costs to the government. Of course having to compete each task brings its own additional costs which don't necessarily make the cost saving proposition true. The big benefit I see to this contract is that it helps prevent vendor lock-in. I don't worry about the next 10 years and $10B, but what happens after 10 years when the DoD is now locked in to proprietary AWS cloud features which make migrating to a different vendor technically and fiscally near impossible.