The tape head is basically a small and really sensitive electromagnet. Magnetized tape creates small disturbances in the magnetic signal. Amplify those disturbances and you get sound. Similar to an antenna, but only works in close proximity.
This also works in reverse. Feed an audio signal through the electromagnet, and the electromagnet will create the disturbances in whatever is next to it. You can do this to record to a tape, or you can do this to pass sound to another tape head, which is how these aux cassettes work.
You can build one yourself really easily. Just take the tape head from a broken player and solder to an aux cable. Take a cassette, remove the tape, and put the tape head in the middle portion so it comes into contact with the player tape head.
I don’t think they care that much. Windows revenue is ~7% , and most of it is probably Windows Server and enterprise/government deals. Source.
Unless SteamOS becomes competitive in the workplace and professional world, it’s just a drop in the ocean, too small to matter.