i think a factor is that a lot of New York small businesses, food trucks, etc. buy from the same local suppliers, and because New York is such a big market, it'

i think a factor is that a lot of New York small businesses, food trucks, etc. buy from the same local suppliers, and because New York is such a big market, it's actually viable for them to only serve one city. The most visible example of this is the blue coffee cups. i'd bet those sausages come from a particular supplier somewhere on Long Island and get sold to many diners in NYC, and that's why they are so distinctive. this is definitely true of the rolls used for the classic sausage-egg-and-cheese-on-a-roll. like, yes, I can buy a breakfast sandwich anywhere in the US, but it will be noticeably different from the New York version, and the New York version will be pretty consistent across many independent bodegas because the ingredients are the same.