When what we think of as the classical guitar was normalized, it was just after luthiers switched from friction pegs like you would see on violins to the geared open-backed pegs, which were the advanced cool new tech at the time. They hit an optimized form early, and couldn't make it better without making an large departure, like steel strings with higher tension, so the guitars that get made are made to be the best and prettiest versions of that.
You can find acoustic guitars with that kind of in-line open-back tuner. I think I own four. But the closed-back style you often see are lubricated for smooth operation. I would guess the post is made from higher-quality metal to keep from being bent from the higher tension, but that's just a guess. There are also locking tuners, but I normally see them on electric guitars with whammy bars, not steel-string acoustics.
I could imagine classical guitars with the more modern tuner styles, as I have seen violins with geared guitar-style tuners and with geared tuners built to look like friction pegs, but musicians often go with their eyes not their ears, and would be likely to avoid guitars that don't look like the ones their heroes played.