Glasses would add another dimension to character building. You can have faces with wrinkles and scars so why not specs? I think they make people look interesting and they are not unattractive in the way old Hollywood movies used to portray them. In my opinion, fringes (bangs) are much more unattractive.

in a medieval setting? Not likely chap. perhaps a looking glass or monacle, but definitely no 'specs'

Maybe the designers decided that it was too modern-looking, like Tiris suggests. Some quick Wikipedia research shows that Nero may have used an emerald as a corrective lens, and folks as early as 1000 AD were using something like glasses to magnify small stuff. Then around 1200 corrective eye glasses started being created.

Then again, maybe the designers started to think about it, and were like "Are these supposed to be totally cosmetic, or have actual corrective value?" and "Do players equip them, or are they permanent features of the face?" and "If the player un-equips glasses, does their vision get blurry?" and "Do we need to put an ophthalmologist in every city now?!" (gives a whole new meaning to the merchant line "Take a look... ") and then they finally said, "Screw it, it's too complicated." Or at least, that's what I like to imagine

Good idea for a mod!

There might be some things like monocles or pince-nez around, but they would be extremely rare and expensive - only the wealthy and/or nobility would be able to afford them. You certainly wouldn't see them on an ordinary peasant.