humans started their first 300k years as nomads – storing was just impossible and decrufing happened by itself when moving along.

So maybe that's why we're not good at it yet.

Sometimes it might be a single field in a 1MB nested structure that you have to remove. So it gets encrypted when the whole structure gets stored and when the field is to be deleted you just throw away the key instead of modifying the entire 1MB just to remove a few kB.

As mentioned, encrypt something and throw a way the key, often called "crypto shredding".