The thing with semiconductor tech, though, is that not only are new nodes faster, they also use less power and (eventually) are cheaper as well. Don't invest in new nodes, and it'll cost more money for the same number of transistors.
It's not as simple as that. You wouldn't make chip with less than a 100 million transistors on TSMC N5. Chips have not only maximal size, but minimal size as well. And you shouldn't forget about horrendous cost of masks. If you need a lot of very small chips for something simple you are better off using something like 28nm or older node. At the end total cost per chip is what matters for such customers, even if cost per transistor is higher. And, IIRC, cost for transistor is currently lower on N6 than on N5.
