Dumbing Down of the US.

The US has long had a strong anti-intellectual tendency, perhaps it is due to populism.  Lately, there has been a dislike of the "educated elite" and their "expertise", which somehow translates into unquestioning acceptance of things which are plain off bullshit.
In this case:  creationism.

Source: National Geographic

 The United States ranks 33rd in the world in acceptance in the scientific notion of evolution. Yes, 33rd! Just ahead of the Turks but behind Cyprus and Latvia. In a 2005 survey adults were asked to respond to the statement: “Human beings, as we know them, developed from earlier species of animals.” Only 40% of U.S. citizens responded, true.
In 2013 another survey asked, “Humans and other living things have evolved over time.” Only 43% of those who identified as Republicans agreed. This was down from 54% in 2009. An 11% decline in 4 years.
Among Democrats 67% answered true while 65% of Independents agreed. Pew’s researchers said party differences remained when other factors — such as the racial and ethnic composition of the political groups, and religious and educational background — were taken into account.
That's pretty bad, but it might explain why other silly beliefs have taken hold in US society.
See also:
Evolution Less Accepted in U.S. Than Other Western Countries, Study Finds