IME, large firms (including government agencies) don't like not having a support contract in place for key infrastructure.

They don't seem to mind open source as such, and will use open source without support contracts for tools that aren't key infrastructure (or for libraries for internally-developed software), and probably wouldn't mind open source with a support contract for key infrastructure (but for a lot of things, proprietary s/w vendors are just better at selling support than the people selling support for open source software.)