...glass bows aren't the only bows in Oblivion or Morrowind. That's just..one type among many.
True, there were also silver bows and steel bows and such...
Yes, I think it would make sense to see some wooden bows, bows don't necessarily have to follow the same progression of materials as other weapons, you can have instead have different types of wood, each with different qualities, and have higher quality wood make for better bows. This way, you still get the material based progression while not having bows made out of metal all over the place.
The problem is, if it were glass, that would make it... glass, and glass is not crystallized, and it only says "glass-like". Overall it is very vague as to what the material truly is.
I think they mean "glass-like" as in like the kind of glass weapons and armor are made out of, and not like the glass you see in you're window, and said Elder Scrolls glass looked crystaline in Morrowind to me. Alternately, Bethesda perhaps just didn't do their research.