Because the large majority of OS only allowed for static linking.
When dynamic linking was finally possible, it was welcomed with pleasure, because not only it allowed to save disk and memory space, it also opened the door for extensibility via plugins, and dynamic behavior without restarts, instead slow IPC with one process per plugin/action.
Now thanks to missteps of glibc design and .so hell on Linux (even worse than on Windows due to all distributions), many devs embrace static linking as some golden solution.
When dynamic linking was finally possible, it was welcomed with pleasure, because not only it allowed to save disk and memory space, it also opened the door for extensibility via plugins, and dynamic behavior without restarts, instead slow IPC with one process per plugin/action.
Now thanks to missteps of glibc design and .so hell on Linux (even worse than on Windows due to all distributions), many devs embrace static linking as some golden solution.