Both Latin and Chinese have been modified by the technology used to write them.

When carved in stone the lines are much straighter. When written with brush or pen they became semi-cursive. When printing was introduced, they became grid-like and regular.

What westerners who are passingly familiar would think of as the standard Chinese typeface - the strict square grid with straight-line characters - arises in part from printing technology. Easy to carve that into wood blocks, and easy to line up the slots into a grid.

Latin was similarly morphed to fit into the realities of printing in the 1500s. And is still being morphed. Notice how numbers 123... are in-line and at the same height as the letters. That's a very modern convention, typewriter and computer influence on our orthography. Traditionally digits were more likely to appear as subscript, off-centre.

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)