Genuine question

As a mixed person, why do people instantly assume my dad is the black parent? I’ve had this happen to me a few times when people find out I’m mixed, and sometimes as an insult like calling my mom a snowbunny or something. My mom is the black parent, so it’s always fun putting them in their place but why do people automatically assume that it’s the mom who’s white and not the dad? Is it some kind of stereotype? Is it specific to me because I’m very light skinned?