A lot of these disputes really boil down to trademark claims (Zorro wasn't described quite the same way in the original book as he is portrayed in the movies) or simply legal bullying, hoping no one calls their bluff (especially in the case of the Conan Doyle estate, since Sherlock Holmes books, TV shows, etc... have been being pumped out for years). The sad part is that these rent-seekers can get away with starting frivolous lawsuits, banking on their ability to outspend their targets. With how long these court cases take and how expensive and difficult it is to make all the legal filings (even if you don't hire a lawyer), they don't have to actually win, they just have to make you go broke.