OEM stands for Original Equipment Manufacturer. A locked OEM prevents the bootloader from being unlocked—preventing your phone from suffering catastrophic failures, which can result from installing bad software or updating software to a faulty version. It can also result from tweaking system files and accidentally changing (or deleting) something that is essential in making your phone work.
Most commonly, these catastrophic failures occur when someone who thinks it’s cool to modify every aspect of their phone—while not knowing about the technical aspects of software—goes on the internet and watches a random tutorial about flashing custom ROMs… only, the process doesn’t go the way they wanted it to, and something terrible happens, like:
Their phone becomes extremely unstable.
They lose all of their data.
Their private information suddenly becomes public information.
Their phone becomes bricked, which essentially means that it’s unusable whatsoever.
So to protect against this, the OEM is locked by default.
For some Android phones, modifying system files and installing software, not from the Google Play Store voids the warranty, so the OEM is locked by default to prevent you from voiding the warranty.
