Do you actually know how much a sub-10nm mask set costs? There’s a lot of speculation from people who don’t have access to those numbers. Those who do are bound by NDAs.
Back in 65nm, 40nm days, big tapeouts were already costing in high 6 figure digits in masks.
And... masks are not the most expensive items on the signoff costs these days.
Specialist verification, outsourced synthesis, layout, analog, physical, test, and other specialist services will easily cost more than the maskset for <40nm.
I would not be surprised if tier 1 fabless already spend $10m+ per design just on them.