"We don't take immigrants"

As an undergraduate student, I would attend career fairs held at my university to find an internship/job. Many companies that come to these fairs are national labs/government agencies that require applicants to be US citizens. I was waiting to talk to a company representative for one such organization. The moment the agent was free, I stepped up to give my elevator pitch. However, before I could begin to speak, the man told me "we don't take immigrants". I was taken aback, and all I could say was "I'm not, I actually grew up in a city close to where your company is located". I went on to give my elevator pitch and try to have a conversation, but the experience left a bad taste in my mouth. I am a headscarf-wearing, brown-skinned South Asian woman, it is hard to tell whether the headscarf or the skin tone (or both) caused the man to assume my immigration status. This happened a few years back, but it is a small event that has larger implications. How many national companies are making such assumptions and limiting the diversity and talent they can bring to their corporations? How many of these corporations are helping shape government policies from an uninformed standpoint related to the make-up of America's melting pot?