I’m assuming it has to do with the way data is stored and how “deleted” data is never truly deleted.
Is this true for other OSs, or just windows?
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Ok imagine a library, it’s a huge library with mobile library vans(USB drives) and even an instant book copier.
But it only has so many shelves.
At the end of each row of shelves(one disk) and on each mobile library van is a big box of index cards. They are far faster to read than the thousands of books. Which are barely sorted. Basically only by the date they were brought in, with new books fit in empty gaps between old whenever possible.
It works really well, you can find any book index card and use it to get the book in seconds.
You decide you don’t need a whole set of books anymore because you just got the 2022 edition.
Instead of going and taking every book from the set out and recycling them you just put their index cards in a smaller box marked “recycling bin”
This lets other librarians know they are allowed to go and put a new book in this spot and get rid of the old one.
You could go and remove the old book but there’s no need right now.
This is a strong analogy for how hard drives work.
They have a file allocation system like an index card sorter that’s literally why old drives were called FAT32 (File Allocation Table 32bit)
Deleting isn’t really deleting unless you delete and clear. The book is still there. Just the index is now in a pile of cards that says “overwrite me first”.
Also ignored in the analogy is the fact our librarian would happily tear books in half to fit the gaps exactly rather than move another book at all. That’s why some disk’s need defragmentation.
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