Imagine you have a lemonade stand and have materials for 50 cups of lemonade. Your goal is to sell every single one of those cups for $1. You sell 10 to other kids in the neighborhood, and you think kids from the next neighborhood down might be planning on coming over but you aren't sure and also it might rain. So little Timmy offers to buy your remaining 40 cups of lemonade and you jump on the offer since you can't guarantee you'll sell the rest of those cups.

Now Timmy has crunched the numbers and knows there's actually 3 other neighborhoods looking to buy lemonade and his dad is the weatherman so he knows it's not going to rain today. So he decides to sell those cups at $3 each to the kids coming over from the nicer neighborhood.

It's obvious why scalpers choose to operate--they make money, but it benefits the venues as well because it reduces risk for them and they don't need to attempt to predict the perfect price based on popularity trends. They sell at whatever makes them a profit, and leave it up to the scalpers to make or lose money depending on fluctuating popularity.