How is that the developer's fault?

You unlock the car with your phone over your data connection and not with a key. Losing the data connection is the equivalent of losing the key. You may not like it, I know I don't, but that's the downside of doing it this way (just like it's a downside to have a physical key because you can lose it too).

I have no doubt that the developers warned management of the risk of doing it this way, they accepted the risk.