Maybe it looks weird now because libraries were collections of subroutines, then have evolved as sub-programs (some spawn their own threads to do their job), an

Maybe it looks weird now because libraries were collections of subroutines, then have evolved as sub-programs (some spawn their own threads to do their job), and then eventually got so big that they became the main program in which you plug your own moving parts: frameworks. Moreover, it is interesting to note that in the same time, the opposite trend exists: some libraries used to be the "meat" of a program, but as connecting two programs in flexible ways is not always easy, that core was extracted and made available directly to other programs. Well-known examples are libCurl and zlib.