I'm going to put David Tweed's comment into an answer, which it deserves.
The dual shorted pins allow inexpensive single-sided boards to be used for X-Y matrices of switches without requiring jumpers.
Here (from an NKK datasheet) are a couple examples of such layouts:
X-Y matrix (This would typically be scanned by a microcontroller or ASIC):
Common line (one side of each switch common, typically it might be connected to Vss or Vdd and a pullup or pulldown resistor (perhaps internal to a chip) would be required for each switch.