We could make cars with bullet-proof glass that would make them extremely difficult to break into, but to most people, the cost is not worth the benefit, so it's not done.
Given the state of encryption technology in the 80s, it's possible that any attempts to secure the protocol would have been rendered pointless by technological advances. Or, it would be more brittle than a non-secure competitor and would have fallen out of use.
We could make cars with bullet-proof glass that would make them extremely difficult to break into, but to most people, the cost is not worth the benefit, so it's not done.
Given the state of encryption technology in the 80s, it's possible that any attempts to secure the protocol would have been rendered pointless by technological advances. Or, it would be more brittle than a non-secure competitor and would have fallen out of use.