Cost, complexity, durability. Just because you can do it on a small scale does make it production worthy.
Plus, when you add all the above together and look at the benefit it can’t be a push.
If you did all that and spent all the money and you end up with the same (or worse) emissions or/and the power increase isn’t there then you just don’t do it.
For decades they’ve been doing pneumatic valve control is some sanctioning bodies. I know one reason why it hasn’t shown up in mass surface transportation is that the rpm needed to see any gain is so high it’s just useless.
That’s not poo pooing anything. That’s understanding what matters. Some guys have no clue (not you RRR).