* The hdd in a phone that is not powered off is mounted. It takes an exploit in OS to pass the Lock Screen or read the RAM.
* The vast majority of people don’t have long alphanumerical passwords. The short pins can be broken.
* Some manufacturing companies don’t handle encryption keys properly. Synology NAS stores the keys next to the encrypted data for automatic access upon boot (unless you change the default and store the keys on an encrypted USB or enter keys manually upon boot).
* There are sometimes bugs in algorithm implementations, especially if a company roles its own crypto with closed source software.
* Sometimes encryption keys are not properly generated. Bad RNGs were a thing for a long time.
* And of course there could be back doors for law enforcement.