I'm pretty sure it is NOT GOG keeping the price high, more so Obsidian or Paradox.
My guess is Paradox, it's literally cheaper to buy the Definitive Edition on sale,
than buying both White March DLCs.

So here's a big Eff you to celebrate your sadistic greed! :the finger:

GOG though still show White March 1 & 2 as available purchases for me despite having purchased the White March Expansion pass which covers both DLC's. On another note the expansion pass for WM1 & 2 is cheaper than both individual DLC's on their own...but if you just want one of them you pay a premium so that isn't so nice.

I bought PoE2 Obsidian edition which covers all the DLC, for -75% discount last year; though it doesn't help if you purchased the base game and wanted just the DLC's later.