I don't because the police could force me to unlock the phone if I used my face or fingerprint. A gesture or password they cannot force from me.
Not that I have any reason to mistrust the police or anything, but ACAB, so, y'know.
Besides, I use Signal for anything good, and set it to erase at the end of each day. So I rarely need to hold out for long.
@oldladyplays @mlanger right? They can still get in, but there's more red tape to get those tools and they are lazy.