Standard construction wood doors have a veneer over a finger-jointed core making it very susceptible to moisture especially in a partially or unprotected doorway.
The stile and rail joints are joined by dowel pins but are only glued at the dowels. Water can get through the coped area because it is not sealed by the glue.
Once moisture begins to get through the coped area, it can lead to moisture infiltration and stile and rail separation.
It can also lead to door swelling, and eventually rot and decay as well as veneer delamination.
Doors with this joinery have only a good durability and should only be used with a full overhang.