Why would you expect smaller transistors to be cheaper?

Because you are paying for silicon, and processes, not transistors. Wafers have a certain cost, and litographic processes can illuminate a certain X mm2 of dies in an hour. If a transistor gets smaller, more of them fit in a certain area.

Granted the machines that make them become more expensive, but that's capital expenditure, which gets amortized as time goes on.

So there are two forces here working against each other.

You are not paying for silicon, lol. The cost of a chip is many, many orders of magnitude more than the raw material cost.

That is what Moore's Law said.

Not really a law though.

Nobody voted for it, that's true. But since reality held closely to it for decades right up to the present, it's reasonable to believe that transistors get smaller and cheaper as time passes.

"Moore's law" is a marketing gimmick. The real physical law that held for decades is Dennard scaling, which stopped to apply already in 2006 once transistors got too small so short channel effects and gate leakage kicked in.

Dennard scaling hit a wall but Moore's Law did not. Worth considering why. One of these is physical and the other is economic.