Because I would rather die than kill. I honestly can't understand how anybody would prefer the opposite. How do you live with yourself knowing that you have killed somebody?
Secondly, this mindset is also considering at in a collision with a larger vehicle, like a truck, the SUV means possible survival, small car means certain death, and the trucker walks away anyway (no, that's not a guarantee but it's heavily implied by the "big is safe" message). The fate of a hypothetical small car is only a subset of possibilities, and also can be mostly discounted because:
Thirdly, if you are driving an urban tank in order to defend against the bad drivers (you being, naturally, a very good driver), anyone who dies in a crash with you killed themselves. It's your job to defend you and yours (going by SUV adverts, they're very photogenic and adoring) from that brutal recklessness.
I don't think it's complicated psychology, even if I think it's extremely misguided.
Not least, the tank is disproportionately a danger to your own kids, has shit visibility and is probably not as safe in a collision as it might feel, leading to a false sense of invulnerability and confidence to push into dangerous situations.
I'm not really sure what you can do to fix it, and anything you could do would be political suicide. I'd like to think if i were in charge, I'd have them banned for urban use by the end of the week, but I'd also be out of office by next Monday.