When it was clear, they’d park her in the middle of nowhere, sit on the hood, and watch the stars… for hours… without saying a word. It never occurred to them that, sure, maybe they never really had a roof and four walls… but they were never, in fact, homeless. 

That’s why Dean doesn’t care about the Impala - because the reason she’s special is because she’s home. Dean loved her and took care of her like a family member because she was always there - family don’t end with blood. But a demon’s got no need for love or family or home … and Dean’s got no need for his Baby.