Why do some people (i.e. white conservatives) think all Spanish speakers (especially native Spanish speakers) are Mexican?

Seriously, I've been called an ILLEGAL for being from a Spanish-speaking country and coming to the U.S. with paperwork. Also, my friend's weird dad saw my name on a social media account when my friend was texting me and he said I was a "typical Mexican". I am a white European Spanish woman, why do people assume I'm automatically Mexican?