Why not license the Cookbook under the GNU Free Documentation License (FDL)?
The FDL is not a free license in the same sense that the GPL or LGPL is. For an explanation of some of these issues, see Why You Shouldn’t Use the GNU FDL or the Draft Debian Position Statement about the GFDL. In particular, if the Cookbook were licensed under the FDL, it would place restrictions on the use of the Cookbook’s explanations of code, in other free software. This would be true even if the Cookbook’s Scheme code were dual-licensed under the LGPL. By requiring that contributions of both documentation and Scheme code to the Cookbook be licensed under the LGPL, we ensure that both documentation and Scheme code can be reused in other contexts which are compatible with the LGPL, including as part of the source code of LGPL libraries.
