That's not to say they make sense. The total amount I spent on having the locksmith let me back in to my apartment that year was significantly less than the cost of putting in a combination lock.
Unlike say etcd where three improves reliability to the best of the three, three locks would decrease reliability to the worst among them.
Then tying that in to be managed by a computer makes it even more handy. When I have family coming over, they can just use their own PINs to get in instead of having to manage yet another physical key. If its an even more one-off allowance to let someone in, I can easily just unlock from my phone. It also makes it easy to have doors automatically lock on a schedule.
I wouldn't want to have to go back to a world where I have to carry house keys with me every time I leave the house. It sounds way less convenient day to day, for the minor effort of swapping some AA's every six months or so for frequently used doors.
So many of my trips I leave with just my phone. Its my car keys. Its my transit pass. Its my money. Its my map. Normally I wouldn't want to take so much extra junk with me every time I'm just going to grab some groceries or getting lunch with a friend or going to the library.
good question. I don't know? There are three things I carry with me literally everywhere: phone, keys, and wallet. Any one of them missing in the morning means I have to hunt around the house to find them before I can leave for work. This would not change if I could unlock my car with my phone (I still need to be able to lock my front door and/or let myself in when I come home again, requiring keys)