The tell-tale file sizeNEF, CR3 and ARW files each carry a small JPEG inside, so the camera has something for its screen. Simple tools extract that, call it recovered and stop, which is how a 50MB frame comes back at 5MB.
Fragmentation is the true obstacleLarge files seldom occupy one unbroken run. A basic carver reads the opening stretch, meets the gap and stops — fine for a small JPEG, useless for RAW or video. Here the fragments are stitched back together according to what each format requires.
Every RAW format is differentCR2 is built on TIFF and tolerates damage well. CR3 uses a newer container that breaks in its own ways. A damaged NEF gives you green and purple bands. ARW, DNG, RAF, ORF and RW2 all need handling the maker’s way. No single tool covers them.
What a delete actually changesUnder FAT and exFAT, deleting or formatting frees the cluster chain and alters nothing further. That is why recovery works at all, and equally why the next photo you take can drop straight onto the one you are trying to save.