Dean likes pie because it comes in all flavors. You could have a variety instead of the same-old-same-old.
Dean likes pie because it reminds him of warm Kansas summers, of soft hugs, and the smell of fresh laundry.
Dean likes pie because it can't remind you of missed birthdays. Dad wanted to come, but there was always some fugly to gank or demonic presence to investigate.
Dean likes pie because it is always an adventure. Sometimes the crust is burnt, or too flaky, and the crumb topping is as hard as a rock, but that's life, right? It makes you appreciate when the filling is deliriously good and the crust is just right.
Dean likes pie because when he eats a bite, the memories of his mother are easy to recall. Out of his 30 years he only knew his mom for four, and Sam didn't know her at all. How twisted is that? Sometimes when Dean can't remember, a bite of pie is the only way to find comfort.
Dean needs pie like he needs the Impala. Pie is his old home; the Impala is his forever home.
Typical Disclaimer Applies.