Because it’s apples to oranges.

Deciding “my typeface won’t have any lowercase letters” is not the same as “my typeface won’t have descenders”. Technically none of them has descenders, but the former compromises by reducing the amount of characters—which keeps every remaining letterform distinct at the expense of reading fluidity—while the latter compromises by distorting a good chunk of letters—making them ambiguous and harder to read.

I very much doubt architects decided “let’s write everything in all caps because that avoids descenders”.

And again, while looking it up I see no end of examples of technical writing with lowercase letters, and they all have descenders.