Look at what goes into a good heirloom tomato... finding the right varieties, letting them ripen perfectly, getting that good olive oil and salt. That's not simple, that's knowing what you're doing. Paying for it means you get the result without the years of learning and the hours of picking through a market. Some people just see the final plate and not the work behind it.
Honestly... it's a tomato salad at a market. People pay for good ingredients and someone making it for them. That guy could just buy the tomatoes and go home. The whole point is you don't have to do the work.