This trope is about how legal issues can prevent creative works from seeing the light of day or that causes their suppression from release.
Many such works are in such a predicament because of disputes over who has the rights to release them. For example, the 1960s Batman series was made by 20th Century Fox. However, Batman is owned by DC Comics which since 1969, has been owned by Warner Bros. who has the rights now to make works involving DC Comics characters.
Marvel also has some legal issues. When it was bought by Disney, the existing licensing deals with the various studios were most unaffected. Disney would later buy back the rights to the Avengers, Iron Man, Thor, and Captain America (These make up the Marvel Cinematic Universe.) from Paramount, but several other studios still have the film rights to other Marvel properties such as 20th Century Fox, who owns the rights to X-Men and The Fantastic Four, and Sony who owns the rights to Spider-Man. As such, its unlikely that there could be a crossover movie with all X-Men and Spider-Man, for example, unless. Another Marvel-related issue with this trope is that the Disney merger led to the end of the animated The Spectacular Spider-Man series; Sony at the time held the film and animation rights to Spider-Man, but returned the animation rights to Marvel in order to keep the film rights. However, various factors prevented Marvel and Disney from continuing that series because Sony owned the rights to their specific version of Spider-Man, which would have forced Disney and Marvel to license it; it would seemingly defeat the purpose to regain the animation rights and license certain rights from Sony. As a result, the show ended because no company could move forward with it.
A common reason for TV shows not being released on home media is music rights. Often, when shows seek the rights to use music, they only get the rights to use it for TV showings. To release the shows on DVD would requiring contacting the rights holders of the music and creating new agreements to use the music. Very often, it is difficult and expensive to gain those rights, so the shows are either never released on home media, or they are released with the music changed or with the scenes featuring the music cut out. MTV had a deal with record companies to use their music for free; this negatively affected shows such as Daria, for example, which was not released on DVD for many years and when it finally was released on DVD, the music was changed. Nowadays, some shows secure the rights to use the music for all forms of distribution.
Some works are legally screwed because they are based on other works. The 1959 film adaptation of Porgy and Bess is one such work. It was produced by Samuel Goldwyn who leased the rights for only 15 years. After that, the rights reverted back to the Gershwin Estate who had control then on out over the film’s distribution. They don’t like the film because it was not faithful enough to the original opera. Ira Gerswhin felt that film disrespected his late brother George’s work; in fact, for years, he resisted offers to adapt it to film because he thought it would be “Hollywoodized.” The music from the original opera was reorchestrated, and much was cut out so that the film would more closely resemble a musical than an opera.. It was pulled from distribution in 1974, and only rarely has it been legally seen public.