Both Panasonic LX10 and Panasonic ZS70 have 20.0 MP resolution sensors but Panasonic LX10's sensor is 1 (13.2 x 8.8 mm ) and Panasonic ZS70's sensor is 1/2.3 (6.17 x 4.55 mm ).
Since Panasonic LX10'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 Panasonic ZS70.
Below you can see the LX10 and ZS70 sensor size comparison.
As seen above, Panasonic LX10 has a 4.1x Larger sensor area than Panasonic ZS70. 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.