The FSF wants the GPL to be a license that people will actually use, and within that constraint, they want it to be interpreted in a way that most strictly prot

The FSF wants the GPL to be a license that people will actually use, and within that constraint, they want it to be interpreted in a way that most strictly protects software freedom, as they see it. If they just wanted it to be as broad as possible, they would be shooting themselves in the feet; it's easy for ticked-off software creators to switch to a less restrictive license if they own the copyright to software under the GPL. This, for example, is why the FSF always mentions explicitly that they do not consider merely using a tool like grep as part of a shell script to be a derived work. They have to be reasonable, or they lose their power.