Every new generation ("node") brings in new lithography equipment
or, if you don't, new lithography challenges as you push into new
process control and equipment limitations. In general you don't
want to live there, but set up for 99.99% yield buy buying the best
you can get. Because low yield is also low reliability and low
predictability, which makes you look clownish.
So that's fresh meat to amortize, on top of the development effort
(paid down at 250nm, maybe not fully at 180nm, short of payback
at 28nm and at 7nm, carrying a hell of a mortgage).
Do not hold onto a belief in rationality re semiconductor pricing in
any aspect - it is supply, demand, sex and fear all rolled up and you
don't get to know who's doing who.
There's also some chance that you are looking at two different
wafer diameters between those nodes or between foundries.
250nm was centered on 8" (200mm),180 /130nm can be found on
8" or 12", depending on foundry.