Felix Salmon wants to know why tacos from food trucks are so damn tasty, and comes down on the side of very fresh tortillas. Kevin Drum concurs. I'm all for fresh tortillas, but I think this doesn't quite get at the structural issue, which has to do with the cost of inputs.
There are, after all, tons of great reasons to eat in a nice restaurant rather than at a taco truck. You get a roof, for example, in case it happens to be raining. You also get walls and a heating or air-conditioning system in case the temperature is unpleasant. You get to sit in some nice comfy chairs to have a conversation with your dining partners while a waitstaff attends to your needs. If it's a restaurant you really like then it'll probably play music you enjoy, have decor that's in line with your tastes, and be at a point on the noisiness spectrum that you find congenial. This is all really good stuff. I don't adhere to the Tyler Cowen school of thought that food is best consumed in the dingiest possible conditions so as to ensure maximum efficiency. That said, if you are single-mindedly focused on the quality of the food then the fact of the matter is that the very low overhead of a food truck means that the only competitive edge available is to make the food good. The real question isn't why the best tacos are often found in trucks (or, in Mexico at least, in little stalls) but why tacos are so well-suited to informal service.
The fact that you can eat them while standing is a big plus. So is the fact that many of the best kind of tacos have slow-cooked ingredients that it's feasible to serve out of a very limited kitchen. Last, the fact that the food cost of tacos is relatively low makes them a viable option for establishments that can't count on cross-subsidy from alcohol to pad the business out.