What point does quindlen make by comparing present -day new york with philadelphia in her father's time

Quidlen is a journalist from The New York Times and she has spent years living in Philadelphia before moving to New York to work for the newspaper company. Philadelphia was not a very good city to liven in during her father's time. The city was full of homeless people and there was no proper waste management. Prostitution was rampant. Present day New York is much cleaner but it still has similarities with old Philadelphia. There are a lot of homeless people and prostitution still thrives.