Almost certainly because you have chosen the wrong raw data settings for the file.
If it is really an AIFF file it should have headers that describe its content making raw import un-necessary. However, depending what exact audio codec it contains you may need to add FFmpeg to your computer to import the file normally. After installing FFmpeg, use File > Import > Audio… or File > Open… and chose the “FFmpeg-compatible files” file type before selecting the file.
If that does not help you could install MediaInfo which should tell you details of the file, assuming it has headers.