clarry: Is it that bizarre?
Back in the day, it was normal to buy a game. And then a year or three later get lucky and find the expansion for it at the bottom of some sale basket in some random supermarket.
The only explanation I can think of is that GOG doesn't want to give tech support for expansions against a base game that isn't a GOG release. And without tech support, their refund policy falls apart...
What's bizarre is that you can't even buy a fucking soundtrack unless you own the base game here.
Well, yeah, that was normal back in the day. Not after the shift to digital, or the last 12 years where DLC has become the norm. We're waaaaaay past the point where that's a plausible expectation.
Agreed on the point about the soundtrack, though. That is a little strange.