Why do the Sparkfun and Adafruit Eagle libraries use smaller footprints than the manufacturer's recommended land pattern?
There are probably different ways to answer this, but my opinion: most Sparkfun and Adafruit customers are probably hobbyists and small manufacturers, who will not necessarily have access to high-volume soldering process. They will probably solder by hand, or use inexpensive automatic soldering systems. So they need more spacing between pads to prevent solder bridges, and make cleaning flux easier.