Dorico works based on the semantics of the music notation. A “note” isn’t just a symbol, it has a duration. In fact a single long “note” might be displayed as many symbols (even extending over several pages) if its duration is several bars, but Dorico still considers it to be “one note”, which what it sounds like when the score is played.
A better analogy with a word processor is inserting something in the middle of a word, not in the middle of a letter.