Inquiring minds want to know! The reason is because pumpkin pies are custards, and custards are very sensitive to temperature. Cracks happen when one region of the pie heats faster than the other. Usually the areas closest to the rim of the pan cook and firm up first. If this happens too abruptly, the outer portion of the cheesecake can shrink and pull away from the softer inner portion. The result: a crack.
The solution is a deep-sided pie pan, and most of the better pie pans sold nowadays have deep sides instead of shallow sides. A traditional shallow-sided pan is much more prone to cracking because the oven heat has an easier time penetrating those narrow regions at the perimeter. In an ideal world all pumpkin pies would be baked in straight-sided forms like tart pans. But then you’d have a tart, not a pie. It’s a subtle distinction I know, but for very American holidays like Thanksgiving, it’s one that makes a big difference.