Quite simply
Nike conducted a research study with the sales of their three tiers of shoes.
Lows
Mids
Hi's
As the study showed, Lows > Mids > Hi's as far as sales went, so therefore, nike stopped producing high top air force ones, simply because they didnot sell as well as the other two, and did not want 3 different variations of af1's on the wall at a time.
Remember, this was the era where white on white's of each would be out within a 3 month span.
the last af1 high, before the whole 25th anniversary mess, was a white high with a gum sole if i remember correctly.
now af1 high is used to promote "Supreme (i.e. barkley 25ths), or QS/limited/rare releases (i.e. bobbito's)
...however, the womens do not count lol