Governments are not big monolithic things, at federal, state and local levels there can be hundreds or thousands of users/endpoints to support. Nobody does that in house, even Fortune 500 companies outsource service and support (that’s how companies like RedHat, Xen, etc got so big when they were still making FOSS software). From another angle it’s about risk reduction, since if something comes up you have a vendor to blame.

you could, but governments tend to be particularly inefficient because they’re very risk-averse. everything they do has to be documented, every decision justified

it’s so risk-averse that it’s a massive risk in fact ;)

outsourcing allows them to say “but it wasn’t us!”