Files are a lot more difficult than entire file systems.
Even shred isn't 100% safe. If I wipe out an entire filesystem, everything is gone.
Oh sure, I need to do multiple reads and writes 1's and 0's, etc... all that helps.
But if I erase a file, sure I can remove it off the disk, at least the place on the disk
where the primary file was. But certain programs like vim and nano cache stuff in memory.
You can reboot, and that will delete what was in RAM, but what about tmp files and cache files?
Then most of us use journaled file systems. EXT4 or XFS or BTRFS are popular, some of the data
you write to disk, also gets written to the journal. ( How do you think file recovery applications work? )
So I have to delete the file, the cache, the journal, any temp files, and whatever may still be in RAM.
Easier said than done. Very few programs do all of this for you at a file level.