Ease of use. I would love if I could just leave key in my pocket and not worry about opening doors or putting it in ignition. I could even connect it to my keychain.
Not that I would be against option to periodically rekey the whole system. Generate new pair of private keys and have the car and key swap them with my approval.
WRT keyless entry, I actually have figured it out. Central wireless lock is cool. It's keyless start that I'm opposed to.