Why the kde2d 3D graph shows a small density not adding up to 100%?


I created a 3D graph with plot_ly in R. However, density on the z-axis is between 0-0.02 which means there is at most 2% of the data at pick points. Actually, 80% of the data has depression value below 10 and Ln income below 4. I am wondering where this data is located. It looks somehow I do not capture them in the density plot. Please see the graph and commands below.

kernel1 <- kde2d(

fig1 <- plot_ly(x=kernel1$x, y=kernel1$y, z=kernel1$z) %>% add_surface() %>% 
  layout(title = 'All sample - Density Depression & Ln Income)


Thanks in advance for your suggestion!