There are at least two main factors that contribute to the changing image of diversity in the US.
First, there is the constant talk of the need to celebrate diversity and to be sensitive to the needs of diverse people. This has helped to cause something of a backlash against the whole idea of diversity.
Second, there is the great increase in immigration over the last few decades. This immigration, which has been largely Hispanic, has changed attitudes about diversity. With the growing influx of Hispanics, many Americans have come to worry that diversity will undermine the essential nature of American society. They worry that diversity has come to mean giving up American society and letting it become excessively influenced by foreign cultures.
These two influences (among others) have contributed to a decline in the image of diversity in the public mind. It has come to be seen by many as a threat to traditional American ways of life.