I’m at a friend’s place and the cat keeps bringing in dead (or half-dead) animals into the house. It’s my understanding that cats think we are big, helpless kittens that don’t know how to hunt. Hence, they think they are doing us a favour.
It seems like a few mice actually escaped and found refuge in some walls in the house, so these “presents” are actually more than just annoying (and smelly if the dead animal ends up behind the couch).
It’s also their way of contributing. You keep getting them food, and contributing to the colony, so they’re also getting food and contributing to the colony, to make sure you don’t go hungry, and the colony is fed.