Cars are excludable and rivalrous property based on the fact they are physical objects that are of a size easy to possess and it is very hard in physical terms for them to not be so.
Patents, on the other hand, are excludable and rivalrous only in the tautological sense. They are defined within law as excludable and rivalrous, so therefore they are excludable and rivalrous.
Patents could be redefined in numerous ways that are not excludable and rivalrous, such as including anyone else who can give reasonable proof that they came up with the idea at the same time or independently. Also, it would not be that great a stretch to limit their transferability, so that they cannot be treated as a normal asset.
Patents, on the other hand, are excludable and rivalrous only in the tautological sense. They are defined within law as excludable and rivalrous, so therefore they are excludable and rivalrous.
Patents could be redefined in numerous ways that are not excludable and rivalrous, such as including anyone else who can give reasonable proof that they came up with the idea at the same time or independently. Also, it would not be that great a stretch to limit their transferability, so that they cannot be treated as a normal asset.