Remember reading an old cooking blog last week that called it a "gravy-soaked crust" tradition from British pub pies. That writer would totally agree with river_hernandez45 about texture being the main point. A crisp bottom on a fruit pie can sometimes fight against the filling. A little give in the crust soaks up the juices, especially in a cherry or peach pie. It turns the whole thing into one soft, warm bite instead of two separate parts.