I haven’t run out of battery on my phone in years. On top of that, these are often stored in what’s called “power reserve”. That’s basically a small amount of battery allocated to the most important things. Even when your battery dies, you can still access things like ID, credit card, home key, and transit card, for around 5 hours.
So what happens if you drop your phone off a bridge? Same thing as if you drop your wallet off a bridge. Except that someone may find the wallet and sell your ID to be used for identity theft.
Phone thefts are way down. It’s really hard to get into a locked phone. And if accessing a credit card isn’t bait enough to steal a phone, an ID won’t be. Wallets DO get stolen though, and there’s no passkey protection on those. Getting new ID and credit cards take way longer than getting a new phone too.