A combination of consolization and cheap padding is a large reason. Not enough buttons on a controller to add F5/F9 plus developers have long figured out that enforced replays of long checkpoint sequences can pad out a 10hr content game to 12-14hr measured game-time.

There's a Ziggurat anniversary sale running which even contains 2 freebies when you own enough of their games. Has this sale been announced anywhere?

I may be deluding myself at this point, but I still hope for some kind of Halloween sale for the weekend.
Outlast is discounted right now, but there are a lot of good horror games on GOG to merit such a sale. A few examples: Doom 3, Diablo, F.E.A.R., The Suffering, Alone in the Dark The New Nightmare, Alan Wake, SIlent Hill The Room, Dead Space, SOMA, The Evil Within, Darkwood, Amnesia, Layers of Fear, Vanishing of Ethan Carter, Penumbra... and a whole bunch of Cthulhu mythos games like Stygian or Dark Corners of the Earth.

So I am wondering when Kerbal Space Program is going on sale...It is on sale on Steam, and while I would rather buy it on GOG, I don't want miss buying it there for $10. Does anyone know if/when it is going on sale here?

Also the fact that checkpoints are the easier and lazier option. You just have a couple of preset points sprinkled throughout the level and that's it. You don't have to program the logic of saving anywhere or making sure everything gets restored as it should. For example loading in the middle of a fight, AI scripts continuing where they left off, physics resuming correctly for objects that were under its effects etc.. Even many games that allow saving anywhere often fail at some of those points. Much less work to just always revert to a clean slate, meaning a checkpoint in this case.

I am more and more convinced that this is this year's Halloween promo. I wish I'm wrong, though.

Price change:
• $11.99 • -20% • Vesper

Being wrong is not always bad. ;-)