I shouldn't have to unlock my garage; it should identify my car by the same way my car identifies my keys as soon as it gets within range, and open automatically.
Think about this for a few more minutes and you will figure out the failure modes. Here's one for free: You can no longer drive past your house without the door opening, at which point you will have to press a button to close the door.
I guess you could have the door close itself when it senses that you've gone out of range. But: what if you own two cars, and the other one is parked in the driveway? Consumers are not going to want to have to solve a logic puzzle to figure out if their garage door is going to be open or closed.