It’s Valve’s responsibility that Microsoft stripped DOS support from their OS in Windows 10?
Starting with Windows 10, the ability to create a MS-DOS startup disk has been removed, and so either a virtual machine running MS-DOS or an older version (in a virtual machine or dual boot) must be used to format a floppy disk, or an image must be obtained from an external source.
It’s Valve’s responsibility that Microsoft stripped DOS support from their OS in Windows 10?