All those major studios listed have their own game engines, so unitys decisions don't affect them anyways. And Epic develops Unreal Engine, so Unitys' loss is their win.
Support for Gwent will end this year and Hearthstone is soon 10 years old and not that relevant for Blizzard. Their much more important game Diablo Immortal uses a different engine.
The big publishers only used that engine for a few offshoots and this change will guarantee that won't happen again.