The reason why devs didn't nerf keys in the mid chapter patch.
The exact same reason is why devs nerfed moris without announcing.
If devs showed key nerfs in the PTB patch notes or announced the significant key changes in some other way, some players would say "KEYS ARE USELESS NOW!1" and would start using all of them before the patch is released. Some time ago they made a mistake and shew Styptic and Syringe changes on he PTB, which resulted in multiple people instahealing themselves during regular matches in live version.
Developers made a very wise decision nerfing moris with no warning, and I am sure they will do the same thing (or almost the same) with keys, we just should wait a little bit.
Still, it doesn't explain why they don't touch Decisive.