One argument could be that they want to provide an AI solution, but maintain some level of control. Copilot can be bundled in with existing licenses, so it's a easier purchase in some sense.

Across the bridge, in Denmark, we've already seen a number of cases where government employees have use various AIs to help them do their job (and in many case used an AI to fail at doing their job). The result has been information about citizens just being entered into whatever AI the employee fancied, without worry about leaking private and sensitive information. I'm not entirely convinced that the public employees strictly speaking needs an AI, but if they are going to use one regardless, it makes sense that it's one that has been approved, whatever that might mean.