Uuuuummmmmm...O I know, save some board space! Yea, i think that's the only thing. And for the producer of the device, shorter testing time, lower pin lost possibilities, and cheaper in production cost.
Less pin devices having lot of advantages. Some of them are listed below.
1. Less immune to noise.
2. Less VCC and GND pins in turn less power consumption
3. Less real estate on PCB
4. Less size
5. Easy handling
6. Cheaper rate
etc...........
If you need more details, don't hesitate to contact me.