Just see that ATM runs windows! Why they don't use Linux?

Because of support and liability.

So you install Ubuntu on an ATM network. Then it stops working. Who is liable for the systematic kernel panic? Well nobody because Ubuntu comes with no warranty. Or the developers who wrote the software for the ATM. But they don't want to be liable, they want to blame it on something else. So they blame it on Windows. Because it's a popular choice.

A solution is to go for a Linux distribution with paid support, but that is far, far more expensive.

Because Microsoft has support plans

Nice!

@StefanH Well, that's just an ontological problem. If they had chosen to use GNU/Linux, they would have developed drivers for it.