I believe the cases of steep sales drop were observed at the moment when a cracked game binary appeared. No game studio would want to spend resources (developers work and licensing cost) implementing anti-piracy for nothing.
They are doing exactly that. Pretty much all research has shown that DRM schemes are ineffective and mostly just cause problems for legitimate users.
The reason for DRM is mostly
1. Cargo culting.
2. Liability ass-covering (we did our best, it's the DRM company fault our game leaked!)
"Company wouldn't do anything unreasonable." is a really unrealistic takes - companies do unreasonable decisions due to managerial cargo cult pretty much constantly and consistently.
that and always-on gameplay generally do the job I think, atleast for games.
This is so true right here. The crackers who break the DRM just find it an amusing puzzle to solve, and the pirates who use what the crackers create never suffer the annoying side effects of the DRM thanks to the crackers work. Legitimate buyers on the other hand have to deal with situations where their paid for game literally won't run for them without a crack being installed because of DRM or broken-by-design anti-cheats.
(I know this from first-hand experience. Some of my paid games run fine after DRM removal cracks are applied, despite breaking in various fun ways prior to that.)
So it would not be surprising to have a similar situation there.
The people who actually make the software are fully aware that any DRM will be cracked within 48 hours of release (with a few small exceptions).
I guess that's also why AAA games are hyped so much before release, so that many people preorder it.
Never thought about it this way, but it does make perfect sense. Thanks!