> Humans, for some reason prefer and know Windows better

Probably because they've been exposed to it in a many settings, for better or for worse. Windows being popular does not imply that Windows is appropriate for any given task.

> Why shouldn't the devices use Windows?

Is this a serious question?

Windows is probably the least stable production OS in the world today.

Windows is extremely bloated compared to an appropriate embedded OS.

Windows is (practically speaking) the only OS where antivirus software is a fact of life. Viruses should not be a concern for medical equipment.

Windows is not even close to real-time.

I don't want to see "Your heart monitor is restarting for updates in 3... 2... 1..."

> and they do it with Windows

This may be technically true, but this in no way implies that Windows is uniquely suited for or appropriate for the task. They could also do it using a PlayStation, but this is probably not an appropriate platform.

The benefit you're describing is just end users already being familiar with the interface because it's running Windows. That's not the case here, the entire interface on this device is of the custom application itself. It doesn't matter that the user already knows that the start button can be used to launch new programs, they're never going to see any hint that the device is built around Windows unless it's broken. There are numerous disadvantages to using Windows for a heart monitor, everyone else has described this to death but the only real benefit to using Windows is that development doesn't require a software developer competent with embedded work. Now they can hire any Tom, Dick, and Harry from the local community college because it's just a Windows app.

Users shouldn't be exposed to the OS here at all.