I have so many world class international students that are very hungry for American professional work experiences (i.e., internships) & they are often told by employers: we do not hire international students. Why?

I have so many world class international students that are very hungry for American professional work experiences (i.e., internships) & they are often told by employers: we do not hire international students. Why? The paperwork? There is none for an international student if they are here legally (i.e., they are given a SS# w/ their student visa). I get it, it is complicated. Some do not have STEM degrees, so there...