> There is zero need for internet-enabled smartness in the garage door opener here.

Yes and no. At the scale Amazon operates, I can see value in being able to automate the process rather than requiring each driver to find and operate the keypad for each garage.

Automation, if implemented perfectly (which it obviously won't be) also prevents one form of bad actor. An Amazon delivery driver who uses your code in the future to gain unauthorized access to your garage. Automation allows this code to be limited to a single use.