People use their phones as social devices, maps, and cameras.

The probability of spilling a drink on them, being out in the rain, or dropping them in a puddle is pretty high. That probability goes up the more a person is outside.

I've never dropped my phone in a bucket of water, but it's definitely gotten absolutely soaked in my pockets when rain suddenly hit or when a faucet in a public bathroom had its pressure set too high and sprayed me like a hose. I've lost a few keyboards to drips of condensation from my cup falling on just a single key, and I'd hate to have my other electronics be that sensitive.