Car insurance is different, because it also covers damages you inflict on others and other people's property.
I am speaking out against mandatory insurance of your own property. Yes, there will be cases where people are underinsured. But mandatory insurance would make some people overinsured.
There is a long argument to be made for balancing this tradeoff, but in short: Owners are in a better position to judge whether they should insure their property than lawmakers and thus it should be up to them (again: as long as their property doesn't have a high probability of damaging other people; in such cases mandatory insurance might be reasonable).
I am speaking out against mandatory insurance of your own property. Yes, there will be cases where people are underinsured. But mandatory insurance would make some people overinsured. There is a long argument to be made for balancing this tradeoff, but in short: Owners are in a better position to judge whether they should insure their property than lawmakers and thus it should be up to them (again: as long as their property doesn't have a high probability of damaging other people; in such cases mandatory insurance might be reasonable).