Windows costs next to nothing these days in the scheme of overall software costs. Office is only a tiny portion of what comes with a M365 subscription, most of which is valuable. Libre office can replace desktop office, but doesn't replace the rest of the integrated stack that Microsoft has.

Until there's competition that goes well beyond just the desktop software Microsoft will continue to win contracts. Having one system, with one login, where everything just works together for everyone is just too valuable.

I use both open source and Microsoft software. If you try to tell me open source is cheaper I'm going to laugh at you. Open source has a cheaper initial price tag, but far more expenses related to configuration, training, and maintenance.