Digital documents are not paper
People have the habit of writing at the end of a digital document. However, it's a just a behavior carried over from physical world of writing on a paper. You can't come back later and decide to add more paragraphs at the top of a letter you've already written.
But in digital documents, there is no such limitation, and it often makes more sense to prepend rather than append.
If it's a journal, for example, entries could be added at the top of the document. This avoids the need to scroll to the bottom every time to add a new entry.
For other content, often the most recent material is most important. You shouldn't have to open and see the first entries, written forever ago, every time.