The GPL is not the only type of 'free' software license, and Linux benefits from software licensed under several other freely-distributable software licenses. By requiring that you put any changes or additions to the GPL'd code you borrowed under the same GPL'd terms, it ensures that no one developer gains any advantage over the other development contributors. This solves problems such as occurred in the original UNIX project. Under the GPL the Linux copyright may be held by Linus Torvalds and others but they have no more right to restrict the use of it than you or Red Hat does. This small burden of lack of restrictive control ensures that Linux and its related technologies will continue to evolve to the equal benefit of all of its users.
Appearances can deceive.
There is in fact a lot of money being invested in Linux development. Commercial Linux companies like Red Hat Software invest directly in Linux both via code that we write and contribute back under the GPL, and money we donate to important Linux development teams like the Free Software Foundation and GNU projects, the LDP and the Linux documentation it is responsible for, and the XFree86 team and their X server. If you have the skills to help write operating system code you also have the skills to install and manage an OS without pull-down menus, dialog boxes, and configuration tools. Features that most people who might benefit from using an advanced operating system require to use it productively. The story of Red Hat Linux illustrates this point.