While csm is also covered by bios, so are many other BIOS-related technologies, which all have their own respective tags. It has enough weight to stand on its own, similar to how usb can stand its weight against computer, even though the latter can very easily cover the former.
If you do add a tag, at least add an excerpt. I saw no information about the tag, saw the question said it was legacy BIOS support in UEFI and so changed it BIOS.
As for changing all tags to computer, we have some pretty ridiculous tag synonmizing: Please undo tag synonymizing: gnome-shell -> gnome, so don't rule it out.