The answer is "the restaurant industry." That's one of the important points of Tomatoland, an informative and somewhat distressing book on industrial tomato production that Bites reported on this summer.
The sub-optimal tomatoes grown in unsustainable ways detailed in the book are knee-jerk year-round additions to burgers and sandwiches, on salad bars, and as garnishes. While tomatoes are integral to some foods (like tabouli), in others, the tomato is there as a spot of red and a touch of sweet-tart.
I asked some local chefs to reimagine winter alternatives to the out-of-season tomato for garnishes sandwiches, burgers and salads.
Martha Stamps of marthastampscatering.com: "I stopped serving 'fresh' tomatoes out of season when I was at The Corner Market. Any tender veggies, like cucumber, squash, avocado, jicama, radishes — are good. Also pickles — okra, peppers, beets, turnips. Lastly, fruit (tomatoes are one, you know!) — sliced mango, pineapple, under-ripe papaya, apples, pears.
Laura WIlson of Nashville Farmers' Market Grow Local Kitchen, formerly of Ombi and The Turnip Truck: "I used to put up a tomato conserve in the fall with bumper crop tomatoes and serve them on Ombi burgers in the winter."
Pickled vegetables, relishes, tangy fruit, cranberry ketchup. Seriously, who needs "fresh" tomatoes this time of year?