Why is that link a "mailto:" link?!
The reason is a combination of:
2 pins is mechanically weak, 4 pins means more options for routing traces past / through the PCB
real-estate under the switch, some switches with the same footprint will be SPDT and need at
least 3 pins anyway. There is a cultural bias in favour of rectangles over triangles/hexagons in
engineering too (for instance the standard QWERTY keyboard can be more logically made from
hexagonal keys rather than square, yet hexagonal key switches are never seen)