The thing about Subway’s sandwiches is that they’re … adequate. If you are trapped somewhere with nothing but fast-food options, and you don’t want to blow most of your day’s calories on something deep-fried or slathered in cheese, there’s always Subway. Your sandwich will be bland, the bread spongey, the cold cuts … well, best not to pry too deeply into the quality of the cold-cuts, because you’re hungry, aren’t you? But it won’t make you sick, and if you’re reasonable about the cheese and the mayonnaise, it won’t make you fat, either.
A few decades ago, “adequate” was a market space where a food purveyor could make some serious money. Subway franchises were a cheap way to own your own business, because they required little in the way of space or fancy equipment, and they required relatively small staffs. And thus the chain grew like wildfire, dominating even McDonalds itself for the title of “most ubiquitous eatery.”