> No agency would voluntarily modernize systems

This is speculative based on an idea that you have about what must be true. It can be shown to be untrue by one example: NASA, NOAA, and other agencies now host applications and data in a cloud environment. Before this, they were hosted at various NASA data centers. You can now search for, download, and operate on data in the cloud. In contrast, twenty-five years ago someone was required to order a physical magnetic tape. They could have kept those systems running, but they didn't.