Why can't the photos in the camera be deleted and always write-protected?

Some cameras have this function: protect photos and don't delete them!

If you want to delete, just unlock the protection of these photos. As for what to unlock, it depends on your own camera. After all, the settings of each camera are different. Anyway, it is nothing more than setting in "Settings or Tools".

There is another way, as upstairs said: formatting the memory card is OK;