How is this an axis? I thought that the opposite of Grim is Cheery and the opposite of Noble is Base (as in being a cad).
It's quite possible to be Cheery Cad (eg Flashman) or Grim Noble (eg Sherlock Holmes)
Topic on Talk:Setting Alignment
Probably supposed to refer to the worldview?
It's fan-speak, it just happened to turn this way. The scales were rather obviously derived from the term "Grimdark", so these two ends were "fixed". Thus it's like this mostly "for historical reasons", which is fairly common for slang.