[nagaiaida]

what selective pressures against oldstyle numerals with ascenders/descenders existed that wouldn't have equally applied to letterforms with those same features?

(aha i have found the answer to my own question: miniaturization for fractions in phototypesetting)

[dhosek]

Not really. The selective pressure really comes well before that: Tabular presentation of numbers, whether that was log/trig tables or railroad time tables, there was a preference for uniform-width and regular height characters for those contexts (this is also why there is a number-width parameter in TT typography to enable a designer to let digits be variable-width in text but still allow tabular setting if desired).

[adgjlsfhk1]

the other part is that numbers and symbols were very much not the priority. The printing press was for books, magazines etc. math remained hand written until the computer

[dhosek]

Nope, not at all. Monotype had a special system for doing math in hot metal typesetting. With handset type it was possible, but very time-consuming. You can find typeset mathematics going back centuries before the computer. There were also (somewhat impractical) systems for setting music with metal type although engraving was more common because of the interactions of lines and symbols.