[imtringued]

This is backwards. PCBs get cheaper to produce the smaller they are, because PCB panels have a fixed size and you can put more PCBs on a single panel if they are smaller. Since you're repeating the same PCB over and over again, it means you're constantly placing the same parts over and over again, meaning that you need fewer reels, which means fewer machines and a shorter assembly line.

The really expensive stuff is through hole components and bulk components (relays, connectors, etc) because they need separate machines (wave soldering, large pick and place).

Placing small components is dirt cheap due to machines like SIPLACE SpeedStar. [0]

[0] https://youtu.be/3joTYHRTcCs

[rcxdude]

There is a point where smaller isn't cheaper, because handling and overhead costs dominate and even get harder. (the same is true for fasteners, where they get cheaper as they get smaller, until the material cost is irrelevant and they start getting more fiddly the manufacture and handle)