Also training techs to repair SMD parts is really easy and cheap, you're grossly overestimating the costs. The real waste comes from boards with designs that can't be repaired so we tolerate a certain yield. For many small devices the yields are shockingly low.
The other thing is that yields are low because of bad designs. If it became uneconomical for you to throw half your boards out then designers would fix their crappy boards with tombstoned jellybean parts because they used shitty footprint libraries. This is a solvable engineering problem and it's gross that it's cheaper to throw shit into a landfill instead of fixing it.
