Because vanilla Generals isn't good enough for you.
The main purpose of this addon is to add disabled in original C&C Generals Zero Hour: Enhanced campaign and challenge. Right now you can replay the original C&C Generals Zero Hour campaign and challenge in more realistic and modern way.
How To Install.
Just extract files from "Data.rar" archive to your main C&C Generals Zero Hour: Enhanced directory. If it will ask you to replace the files, press "Yes To All".