In the end price discovery is supply/demand, and it appears investment in DRAM manufacturing is focused on improving RAM performance, and just keeping up with demand, not outpacing it.
Since the barrier to entry is very high, there's not so much pressure to compete further on price.
While it's true that the market ultimately determines pricing, the fact that manufacturers can stuff larger amounts of RAM into the newer equivalent SKUs means the price per GB for fast memory would still be driven down. This is even possible if new unit prices are higher, i.e. if this year's "entry-level" SKU costs a little more than last year's but now has more capacity.
Since the barrier to entry is very high, there's not so much pressure to compete further on price.