It makes sense. Jesus offered Himself as our Supreme sacrifice so animal sacrifices are no longer necessary.
Cain's offering of vegetable/fruit produce wasnt accepted by God also because it was not given with a spirit of sacrifice. it didnt cost Cain anything. With Abel it did- also the heartbreak of killing an animal he, no doubt, became attached to.
When the person made the animal sacrifice, if they were sincere about it with God, sacrificing thier first born calves and lambs would have had a heartbreaking effect on the person- it really was a sacrifice of the heart.
Later it became a routine and tradition -- and they were even selling these animals in the Temple for sacrifices.
PS-- I personally believe that there is a place for animals in Heaven-- so even these animals that were sacrificed are in Heaven right now