It probably doesn't bother cops that much.
* All the logs and system files will be plain text. So cops can still know when you took a picture, or made a call, or installed an app.
* All the cloud based storage your phone connects to is stored plaintext and accessible with a warrant.
* All the metadata on the phone network is accessible - phone logs, text messages, internet access, IP addresses etc.
* Certain apps might leave information laying around in a readable format, either locally or on their servers.
* PINs, biometrics and even most passwords can be cracked very easily. I doubt many people enter a strong passphrase into a phone. I doubt alternative schemes like Google's pin board thing or Microsoft's picture login are much better (both might be inferable just by dusting the screen).
So yeah you could encrypt your private data with your finger print. And it might require a modicum of effort to get at that data. But it's not insurmountable and I expect police forces are not especially perturbed.