So, we all know Dean loves pie. It’s a thing. I’m not sure what to say to you if you don’t already know this.
But it’s not like Dean likes pie just because pie is awesome and delicious. Why do I think this?
In Dark Side of the Moon, we got a glimpse into some of the memories Dean and Sam hold dearly, would be part of their “greatest hits”. One of Dean’s memories was with his mother. She had baked a pie during the memory and she had asked Dean if he wanted a slice.
I think pie reminds Dean of comfort. Pie reminds Dean of his mother, someone who understood him and accepted his high level of empathy as a child, allowed Dean to be emotional. Pie ties into home, the only home Dean knew before he and Sam found the Bunker.
I believe Dean does not just love pie just because of it’s taste. I think Dean loves pie because it’s one of the only things that would tie him back to his mother, someone who represented a time where it was okay for Dean to portray his emotions in a healthy way as a child, something that ties in to a time where Dean didn’t have to take care of his brother or worry about the monsters lurking in the dark.