Because they are low-paying, internships tend to cater more to privileged students.

Internships are designed to help college students build up their résumés to get jobs after college.

Yet interns tend to be the lowest-paid position in an office. The average intern salary in the US is around $12 an hour, according to Indeed. That wage cannot pay for a one-bedroom apartment in most of the country, let alone in the major cities where white-collar internships tend to cluster.

Since these programs often don't pay much (or sometimes at all), many low-income students cannot afford to take an internship, said Matthew Hora, an assistant professor at the University of Wisconsin-Madison.

Plus, students aged between 25 and 34 increased by 35% from 2001 to 2015. This number is expected to grow even more in the coming years, as workers want to keep pace with rapidly changing technology. Many of these older learners have families to take care of, Hora says, meaning they don't have the option of taking time off from their jobs for an internship.

"If internships are only accessible for students who aren't working or have parental support, if that kind of lack of access continues to happen, you're just going to see a reproduction of privilege," Hora told Business Insider.