That is because Lapti Nek film version is lost forever except for as it appears in the film itself. The music master tape could not be found anywhere in the Lucas archives.
It may have been borowed Like the Master for the Jabba scene during the making of From Star Wars to Jedi. And now since both are permanently Lost.
Lapti Nek exists only with the film. Been so long since i have seen Return of the Jedi, i believe the problem is Jabbas and Oolas Huttese dialogue is mixed in with the music.
I am sure fans and bootleggers have tried making a clean version of this from this souce and given up in despair.
The only thing That could be done if Lucasfilm cared was to re-record it from the original music sheets, that is if the artist who sang it is still even available. But they did not do so because they now had Jedi Rocks the only piece of Music written for the special editions not by John Williams.
Williams wrote that new end piece in Jedi that goes "ya ya ya ya ya." Instead of Yub NUB, or yub yub.
There was also an LP with the dance version and Disco version of lapti nek, as well as the album version. That with the film version means their are 4 versions of the song.
There are 2 versions of Leia Breaks the News, and 2 Versions of Funeral Pyre for a Jedi. 2 versions of The ewok Celebration song and 2 versions of the forrest battle. The ewok Forrest battle not used in the movie is the concert suite version.
Even if you have the anthology and the rca or sony versions you still don't have all the music, but close to it. Much closer to a complete scores than say for all 4 indiana jones scores released recently which are missing hours of material in that boxset. The prequels scores are also incomplete much more so than the original trilogy music. The original trilogy music is a lot more played and popular and has way more re-recordings than the prequels. The Public consensus seems to be that the prequel scores were not as good.
In fact the only Modern Scores that come close to dupliacted the quality of the oot scores are those by Howard Shore for the Lord of the Rings Trilogy. Not sure everyone would agree with that, or that the movie trilogy of lord of the rings is the modern equivalent of the immortal trilogy that star wars once was. Before the dark times, before the gout.