A question about jack o' lanterns?

Is there a reason we cut the top off the pumpkin, clean it out and set the top back on as opposed to cutting the bottom out, and pulling the pumpkin off the base. It seems to me this woul make it easier to clean out as you could cut a bigger hole, you could put the candle on the bottom without reaching your hand in, and it would make the pumpkin look "cooler", more complete because there wouldn't be a hole in the top of the head and you could grab it by the handle. Maybe there's a practical reason this isn't a good thing, maybe it's just tradition. If it is just tradition, how did the tradition come about? What do you have to say about it?