I think one of the reasons for why the GPL as once more popular than other licenses has to do with the fact that it was created for the GNU operating system, basically a collection of simple command line utilities. No one would think of using these in other ways than to run them on the command line (or in a batch file), which is explicitly excluded from the “derivative work” concept of the GPL.

Things got complicated once people put libraries under the GPL, which is when all the legal uncertainties cropped up about what constitutes derivative work.