Since AI is heavily parallelizable, it only matters that cost(as in dollars) will keep exponentially decreasing.

It doesn't matter if you can't double the transistor density of a single cpu if you can just double the number of machines. At the end of the day you still managed to double performance for the same price.

See https://en.wikipedia.org/wiki/FLOPS#Hardware_costs (note: in another thread someone noted that this wiki is outdated/inaccurate. If anyone have the relevant expertise they should help edit it)