Tighter emmisions standards
Believe me, if the manufacturers could have done this easier and simplier, "they would have." Honda, for example, experimented with (don't remember what it was called) a separate burn chamber in the head. Basically, the car manufacturers were brought kicking and screaming to the "emissions table" just like they were brought "kicking and screaming" to the "safety table."
Nobody cared about "you." "They" that is, "the thems" only cared about emissions (govt) and "the bottom line" (manufacturers)