Because when the average person hears "the government owes x Billion Dollars" the assumption is "they will be handing over X billion in cash". It's like the Ukraine military support - people hear "3 billion USD in military aid for Ukraine" and think the US is handing over 3 billion dollars, not handing over about 3 billion worth of old soon-to-be-retired equipment.

Which makes conversations about government debt really fun. It's just a lack of understanding.