Why did Romans think Rome was the center of the world?

Because at that time, it was. Think of a world where there are no airplanes; that the average travel is by beast of burden. Then think of the marvelous news that came from this exotic, cultural place called Rome. Those who went and came back told incredible tales. If you were a citizen, you were afforded certain rights not given to many others. Rome was financially, scientifically and legally important. Rome has influenced almost all facets of our lives, including the calendar we use, the wedding cakes we cut and the wreaths we hang out at Christmas. Oh, and by the way, Christmas was originally Sol Invictus, a Roman holiday. If you are a June bride, you are following the June tradition of marrying under the benevolent auspices of Juno. Let's also mention that they have the greatest food on earth. When in Rome... and out of it... we still do as the Romans.