Both Ricoh WG-6 and Sony RX100 II have 20.0 MP resolution sensors but Ricoh WG-6's sensor is 1/2.3" (6.17 x 4.55 mm ) and Sony RX100 II's sensor is 1-inch (13.2 x 8.8 mm ).
Since Sony RX100 II's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Ricoh WG-6.
Below you can see the WG-6 and RX100 II sensor size comparison.
As seen above, Sony RX100 II has a 4.1x Larger sensor area than Ricoh WG-6. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.