Linux is open source and therefore its source code is available to everyone on the planet. However, the trademark on the name “Linux” rests with its creator, Linus Torvalds.
The source code for Linux is under copyright by its many individual contributors, and licensed under the GPLv2 license.
Because Linux has been a community project therefore, it has a large number of contributors that kept growing over so many years, contacting each individual contributor and getting them to agree to a new license terms & conditions is virtually impossible and so, Linux is distributed under the GPLv2 license to the users and companies.