> Why can’t I snap a picture of a written WiFi password to connect to WiFi?

You can actually do that, as of last year's iOS release. It's sort of a pain, but it's doable.

You need to be at the point where it's asking you for the WiFi password, tap the text field, choose "AutoFill", choose "scan text", and use the camera interface to pick the text.

This is extremely undiscoverable, no argument, but it is at least a system-wide standard for how to scan in arbitrary text when you have a text input. (They've picked "AutoFill" as the brand-name for all their get-text-from-somewhere-else features, so it also contains standard password-filling from apps.)