Venom is the new movie made in partnership with Marvel Comics who introduced and created the comic book characters including those that are in this movie which are Carnage and Venom. Usually, when a movie is made, it is done so that money is made. When a character is written or introduced, many companies want the rights to that character because people will now know and identify that character based on its popularity.
I believe that Venom was created mainly for the money it wants to make as people pay to see the movie in the theaters and not necessarily due to the character rights. However, only time will tell if other movies are made by Sony Studios in association with Marvel Comics.