They optimize for small batch development costs. Slapping windows PC when you sell a few hundred to thousand units is actually pretty cheap. Software itself is probably same order of magnitude, cheaper for UI itself...
And cheap both short and long term. Microsoft has 10 year lifecycles you don't need to pay extra for. Linux you need IT staff to upgrade it every 3 years. Not to mention hiring engineers to recompile software every 3 years with the distro upgrade.
I would imagine they used specialized controller cards or something like that.