Decompiling is not same as pirating though.

In order do decompile you already need a game. If you usually buy games you'd still buy one. If you pirate games - you'd still pirate it.

So doesn't seem clear to me if there is a lot of lost revenue here?

And pirates don't really need AI do hack a game etc. All possible games have been on torrent trackers since forever.

Possibly ability to decompile and modify it would be a free marketing (from those who mod it and post videos) and only increase sales. Potentially what games should do is optimize builds for this so that mods can be easily created and shared - e.g. you buy a game and apply a bunch of mods created by ai or not.

The only reason I see is when it can hurt sales if some cool mod someone does can't be easily applied to original game and then you have no choice but to pirate it in order to play that mod.