Has this old term never entered the argument for keywording milling?

Lots of invested players want it.
Wotc don't - because apart from this one card, what the heck does the term "Mill" have to do with either "Discard a card" or with "Forget a spell". It's not discoverable or memorable for new players; which is the whole point of a keyword.

It's also not something you put heavily enough in a set as a theme to warrant a keyword that way. (Because how horrible would a set be where one in four commons includes a forced discard?)

Bury is probably off limits because it already appears on a bunch of cards meaning something else

Well, it kinda is ok here because you're specifying where it's coming from; and it's using the same meaning of bury "send directly to graveyard, cannot regenerate" so maybe?

I'm a champion for bury.

I bring it up in Introducing new Wording.

As I did before, I'll point out that Call of the Wild already used "bury" in the sense of putting a card from the library into the graveyard.

If you go through my cards you can also find dude1818 repeatedly pointing out incorrectly that bury already means something different and apparently not once having read my reply. :)

Huh. You know, I did read through that conversation before. Totally forgot about the talk of milling. Must have planted some seeds in my mind. I posted this while looking through some old cards, found another used in a similar manner to call of the wild