Copyright issues. A certain copyright owner has exclusive copyright. The music itself has not been officially released and has not been included by various copyright agencies and record companies. Some music could be found on the Internet a few years ago or more than ten years ago, but later it became official and became unavailable. This is mostly the reason. The music is presented live, there is no studio version, or there is no high-quality live recording version. This is the case with most contemporary large-scale musical works, which can only be heard at concerts. The work itself still exists in documentary form and has not been given the opportunity to be recorded or released. For example, some traditional music has scores, but there are no performance recordings. Even how to perform the scores cannot fully reproduce the original historical appearance of the music. You can't find it on the Internet, search engines are not omnipotent. Some music may be buried under duplicate names or other versions.