Why are there so many clinical research positions open in the United States? (over 80,000 on Indeed as of April 2019)

The clinical research industry is booming in the United States, and around the world. More trials are being registered than ever before. In addition to new federal legislation such as the 21st Century Cures Act that opened new funding for more trials on rare diseases, pharmaceutical companies and investors are eager to continue their drug and medical device development, and flood billions of dollars into the clinical research industry to test their experimental treatments.