if you look at an old remmy; such as a 600 or 660 or 788, you will clearly see why- cost. some of these older sights have multiple rear parts, and even the front can be costly. Say a old remmy 788 front site- usually a giant sharkfin sight, fully ramped, ramp is fully cross cut to stop sunglare, usually has 2 screwholes through it, which also has to then be done to the bbl, and perfectly straight at that, and perfectly at the right depth. then the front site itself needs to be made perfectly square, and then what if the front site has a skinny post, with a bead aiming point? and the bead aiming point is either a piece of brass, or a mother of pearl dot?
You see, and we have just barely talked about the front site, forget a good rear site, that is clearly marked, numbered, with correct measurements for field useage; and 2 precision screw sets to carefully set your windage and elevation, and that they are easy to adjust, and then lock down like cement, when you are done and tightening them down.
scopes will not last forever, and sights will almost allways be faster to sight, on moving targets, except for reddots; It is good to know how to use sights, and I myself won't own a rifle that does
not have them; but that's just me...