Because no human is born empathetic...
Everyone needs to be in a safe environment and have someone teach them empathetic.
Not understanding that, especially if you were lucky enough to be safe and have someone teach you...
Is a million times worse. And usually just means you're not really empathetic, just a veneer of it.
If someone is actually empathetic, they don't need to ask rheyorical questions about why some people have zero empathy.
That's literally what empathy is, which I honestly think might be the root of your confusion. You don't know what the actual word even means, you're just going off how others use it without understanding it.