Based on an inflation calculator, $4000 in 1993 is $6600 today, but how many games are actually $9000, used or new?
In addition, the economies of scale are smaller with a pinball industry that sells, what, 10000 games per year, compared to one that sold 5-10 times that. The model of more expensive LE variants also make some models more expensive.
I would also argue that the programming and rules of most modern machines would require much more effort than the 90s machines did.