Sorry, but you are very wrong. The costs if emissions equip on diesels is quite high as they are very difficult to clean up. Gas engines are a breeze by comparison. The solutions tor diesels are also pretty poor, but it us all they can figure out for now. Having to add DEF is a poor engineering solution, but it is the best there is for now.
Hopefully, someone creates the breakthrough like they did on 2strokes a few years back. They went to a new stratified combustion/intake and cleaned them up a bunch, mostly ht burning a lot more of the gas going into the cyl. Nit to imply this is a solution for diesels, just the innovation process that created a dramatic technology shift...