Some of the Linux copyright holders are dead. Some have merely vanished. One of them's a
company that tried to kill Linux a few years ago. In some cases we probably don't even have a
solid idea who the copyright holder is. Changing the license isn't a real possibility.
(The last time the license changed was in 1992, when it probably was possible to identify
everyone who'd contributed any code to Linux using a single person's fingers. Since then Linus
has clarified what his interpretation of the license is at various points, but these
clarifications aren't binding)