Because you don't know fully how that information is being used or how it can be used for in the future. The information might seem harmless and unimportant, but what if it's not in the future?

Social security numbers weren't initially heavily protected information. My father's university used his social security number as his college-Id number. He had to write it on all his exams. His name and his ID number were even on public rosters. Today, getting someone's SS# opens them up for identity theft, tax fraud, and a whole bunch of issues. That's why you should care. Any information they collect on you is more information that could potentially be used to hurt you or your family in the future. And for what, so you can chuckle at a girl falling on her face while lip syncing mariah carey?