At first, the numbers appear reassuring–the U.S. remains the top destination for foreign science, technology, engineering and mathematics (STEM) professionals. But lurking deeper in the data is a second, troubling statistic: Fewer of these bright workers are migrating to the U.S. each year. Instead, they’re putting down roots in East Asia and other growing regions.

The numbers come from a new study led by LinkedIn, Stanford University and other institutions in the U.S. and Europe. The study parsed LinkedIn users’ work histories stretching over two-and-a-half decades, focusing on professionals in the computer, mathematics, engineering and architecture fields. The findings? In the ‘90s, these professionals were increasingly likely to leave home and make their way to the U.S.–but the probability of STEM workers migrating to the U.S. dropped from 37% to 15% between 2000 and 2012, according to the study. (The probability of non-STEM workers migrating dipped from 25% to 13%–not as steep a decline.)

Emilio Zagheni, an assistant professor at University of Washington who co-authored the study, says LinkedIn’s insight was startling. “Although the general trend was not surprising, we were quite surprised by the size of the change in the U.S. with respect to other regions of the world,” he said.

The study suggests a series of causes for the plunge, like 2008’s financial crisis, the dot-com bubble, and–perhaps most responsible–the U.S.’s stricter immigration laws. The latter is one immigrants like Shayan Zadeh can attest to. Zadeh is an Iranian immigrant who came to the U.S. to pursue a Masters and PhD in computer science, and eventually co-founded the online dating site Zoosk.

“The visa process, the immigration process and how broken that system is–it has become a lot harder than it used to be 10 or 15 years ago to [immigrate],” Zadeh said. “At the same time, other countries have really stepped up and made that process easier.”

Shobana Radhakrishnan–vice president of engineering at Mindflash, and a former engineer at Yahoo and Netflix–immigrated from India to the U.S. in 1997 to earn a Master’s degree in computer science. Radhakrishnan predicts that as nations in Asia develop more robust STEM infrastructure, fewer professionals will opt to pick up and travel to the U.S.

“In countries like India, there has been a huge boom in the IT industry, providing very compelling opportunities for job satisfaction and career growth,” she said. “In addition, several foreign universities are in partnerships with U.S. universities… that allow students to get credits from U.S. universities in advanced areas of education while residing in their own countries.”