We're in the same boat. And for a few month I've found it pretty annoying and I've tried to stop, but I haven't manage to do so. What's wrong with our brains?!
The error with your brain is that it thinks that a behavior which has been genetically engineered over millenia to be the most effective way to interact with your children should be consistent with/follow the same rules as you use in adult conversation.
I think parents do this as a (subconscious?) way to help frame things from the child's perspective, knowing that the kid is terrible at taking on anyone else's perspective.
It’s papa that is tired, not me.