> If he can come along and sell the tickets for a markup, why won't the sellers sell directly to the buyers and capture that whole amount for themselves?

I imagine the event wants to fill as many seats as they can. In addition to ticket prices, they also have food, drinks, merchandise, parking, etc. to sell.

If a scalper buys five face value tickets at $50, they would only need to sell two at $150 (3x prices are common) to profit. Even if they don't sell the other three, they've made money.

So the way I see it:

Venue: Loses food/merch sales for 3 people

Fans: 3 people weren't able to attend (tickets gone, can't/won't afford/buy inflated price)

Scalper: Made $50