So how come . . .

Bifocal spectacles have the lower portion of the lenses cut to a higher magnification, so someone with weaker muscles in the eye can focus more easily on fine print that is close to the eyes.

All well and good, I suppose, as long as the reader holds his head upright and trains himself to look downward. Then a good portion of his visual field is magnified, even though only the reading material that needs magnification is only a small sub-portion of that portion of the visual field. For other visual tasks at greater distances, the added magnification is useless and even gets in the way.

Bifocals could be made less awkward by limiting them to the field of view that a reader is likely to need. To wit, if the magnification is needed only for materials that are closer, then put the magnification in the area of the lenses that both eyes will be looking through when they are focused on closer objects. Eyes converge---point inward---on nearer material. So move the magnification areas closer to the nose, a little higher, and a lot smaller. They'll be where the eyes need them when reading, and out of the way for distant vision or for tracking moving objects.

If I get time I'll sketch what I mean.