I think on closer monitoring over time you will see it is a combination of two mlc traits.
1. Yes, they forget and don't even know it. We don't know why cuz when we ask them, they don't remember.
2. They do exist in a different time (zone) warp. Their mental and biological clocks have virtually stopped. Their existence is without a timeline, other than the last thought that crossed their mind, or the timing of the next entertaining event they have become focussed on in advance. We would consider it a distraction. They consider it their reason for living.
Notice I refer to them as existing, they think they are living. Are you beginning to see the conflict in behavior vs expectations?
More and more you will read posts by people who have ceased to depend on their MLCer to do things on time that they are supposed to, or to even help with the family needs in general. Trying to enforce adherence can become more exhausting than just making other arrangements and concessions of your own.
I hope you can make some adjustments that work with your H, without having to just leave him alone to his free will.