The most likely reason is that you are importing classical music. Unfortunately there are so many additional factors involved in getting a perfect match (Orchestra, Conductor etc) that partial matches are as good as you can hope for on most classical tracks.
The other common reason why you might not get a match is that the track simply isn’t available in Apple Music yet.
If you think Playlisty has missed a simple match with a track you know is there in Apple Music, please send us details using the form below, and we will try to fix it!