Because they're slightly less and I can most likely have it shipped from another store just as I could from GunBroker and avoid paying the fee. Not to mention I wont be dealing with multiple sources, as in, I dont want the possibility of something getting mixed up and GunBroker telling me to talk to BassPro and BassPro telling me to call GunBroker.
At the end of the day BassPro has decent available inventory you just cant rely on their employees to be more knowledgeable if you sit on forums all day and read about things. It's like BestBuy of the gun world.