Indeed, I suppose that many LW patrons consider PUAs to be manipulative and immoral, and don't use PUA advice for that reason.

I'm yet to see someone who has the skills but doesn't use them for moral reasons. While it's possible to use them immorally, there's nothing about PUA skills that's inherently immoral.

Also, don't forget that LW might have a large number of atomistic loners who don't want to be in relationships, and this might contribute to the high percentage of singles.

It would require a vast deviation from human emotions not to want any kind of relationship (committed or casual, sexual or romantic etc.) with any partner whatsoever. The more likely explanation is that they don't want the kind of relationships with the kind of partners they think they can get, which is basically lack of skills together with perhaps too much rationalization (which is considered wrong thing to do on this site).