It's simple forecasting and seeing that they probably won't sell. Stern wouldn't make one, but maybe a boutique may come to fruition one day.
The main problems are that not only does a head-to-head require a lot of space, but it requires 2 and only 2 people. Meanwhile, pinball can accommodate anywhere between 1-4 people at any given time, while taking up less space.
In another thread, I saw someone suggesting getting a Chexx over what I think was a Stranger Things. I recently did something similar, I got rid of my 4th pin I had in my basement and got a Chexx. The problem is that it's freggin way bigger than I thought! It's like 9' required for the game and space for both players (and it's wider too!). Therefore it's sort of the middle of the room instead up against a wall like pinball. Then you always need that 2nd person to play, and I'm sure many of us go to our game rooms alone more often than not. Chexx is cheaper than a NIB which is cool, but a head-to-head pinball will be just as expensive so it doesn't have that advantage either.