It sounds like from the forum that some people rely on only the app, and Tesla markets this as an option. Seems like a big issue to push that feature and then for it to be down for hours.
Some people are just like that. I have a friend who drives a different brand that has a similar feature, and he uses the app almost exclusively, even though getting to it and waiting for it to go through takes far longer than me using my fob. He just really likes doing it the "high tech" way and only using one gadget for everything.
Who makes an app to unlock the car when you're carrying the key? You could also run out of car charge, but youre not worried about that, both you can just look at the gauge.
My phone battery lasts all day, and the internet is rarely down; but servers on the other hand...
I can't imagine anyone using the app to unlock their car on a normal basis. Normally, you just walk up to it with your phone with bluetooth enabled, and it unlocks for you(you don't need to proactively take an action on the app like clicking an unlock button)
So, you carry the keycard in your wallet in case your phone dies or it is stolen or whatever, you can still get in and start your car. But 99.999% of times you just walk up to your car and start driving without unlocking, or turning a key, or anything like that.
The keycard is just a back-up that you can keep in your wallet. Unlocking with the app (phone) happens automatically with bluetooth when you are near the car, no internet required.
The main reason to use the app is if you want to unlock remotely for someone else using your car.