So a single point of failure then?

It also means you are holding your cards on your time all the time you use your phone on the street, which is prime time for somebody to come and snag it out of your hand

it looks like a normal case, you can't see the cards.

not a single point at all, it's just a couple cards in the slot.

It's still a single point of failure.

So now if you lose your phone you also lose your wallet and are really screwed. It’s better to hedge your risk and keep important stufd in different places. It might increase the chance of losing something but mitigates the risk of losing everything. I think most people would prefer to mitigate the big risk instead of the small ones.

Also would make cancelling your cards harder if they were lost along with your phone?

I don't call banks, it's a terrible experience. I always use online chat or Twitter for that sort of thing.