Maybe for text specifically you're right, but we use screens for other media like pictures and video. If we have to tone down contrast to make high-contrast text comfortable, we are also reducing contrast of other media, and this loss may be significant.
Now, if we had reflective monitors (like e-ink etc) we could just be comfortable with maximum contrast text (like printed text). I think the display technology is a problem here.
(But still: there are some books with yellowish pages which I find more comfortable to read than ultrawhite pages. Maybe such lower contrast pages are more expensive or something, or not adequate for all lightning conditions etc)
Now, if we had reflective monitors (like e-ink etc) we could just be comfortable with maximum contrast text (like printed text). I think the display technology is a problem here.
(But still: there are some books with yellowish pages which I find more comfortable to read than ultrawhite pages. Maybe such lower contrast pages are more expensive or something, or not adequate for all lightning conditions etc)