Well, I don’t know about the OP, but here in Chicago, within a mile of my house I can find small, family-owned restaurants featuring more than a dozen different cuisines. This was not the case 20 years ago, when I was growing up. Even the regular supermarkets, not just the ethnic markets, carry a far wider variety of foods from around the globe than they did even 5 or 10 years ago, and I quite like it that way, myself. I hardly ever buy groceries at chain places (or much of anything at chain places, except canned goods, cleaning supplies, and cat food) for that matter, because the prices, variety, and service are so much better at the ethnic and family-run places around here that there’s no point.
And if I, born and raised in the U.S., find ethnic markets and restaurants fascinating, convenient, and cheap, immigrants do to a much larger extent. The Vietnamese neighborhood 3 blocks from me attracts shoppers from all over the Midwest, as one can easily see by the license plates on weekends especially. The same is true of the Indian/Pakistani neighborhood a couple of miles from here, and of the Middle Eastern bakery/groceries a couple of blocks in the other direction. I’ll never understand why people in my neighborhood buy fresh produce in Jewel, when they can literally walk acorss the street to the Mexican family-owned produce stand and buy produce that is twice as fresh, for half the price.
When I lived in Bloomington, Indiana, I was very homesick for city diversity, and although we were in the middle of a farming region, somehow fresh vegetables and dairy products were much more expensive than they were in Chicago, frequently twice as expensive. Sometimes competition is a good thing for consumers, and the ethnic markets were a missing ingredient in Bloomington, a town with a couple of supermarkets and a natural foods market, but where I never saw a single produce stand, or even a full-service bakery. If you didn’t like the limited selection at the supermarkets, or didn’t want to pay double or triple for organic food, you were S.O.L. I used to load up my car with groceries every time I went home…how is it possible that there’s a college town where until recently, it was impossible to buy a decent cup of coffee or a real bagel?
And to the O.P.: where are you getting your information that immigrants aren’t opening as many business as they used to, or that immigrant-owned businesses are dying out en masse and being replaced by McDonald’s and Wal-Mart? I can imagine it happening in some isolated areas, but I see more diversity in the consumer market, not less. (And no, I haven’t spent my entire life not setting foot outside major cities.)