LOL, if they did what you wanted and made it impossible to add tracks multiple time, then you would have people complaining that they can’t add tracks multiple times.
At least this way they are giving more control rather than less control of what is in your playlist.
As @Suedkiez says the improver is the method to clean up the playlist if needed.
There is a video that goes over the improver in this post:
Note: the “improver” only shows up if there are things to be improved… so not all playlists will have the option to improve it.