There are two reasons why this may occur.
1. Some layers are too detailed to draw when you are zoomed out to view a large area. Below the name of each layer, you’ll see “Zoom Levels: [#-##]” which indicates how close you need to be zoomed in before the layer will start to draw. You can see your current zoom level at the top centre of the map, 1 being the farthest out, 20 being the closest in. Zoom in so your map is within the zoom level range indicated by the particular layer to see it draw.
2. Not all layers cover all geographic areas. Check the coverage map to see the geographic extents of each individual layer. If your area of interest falls outside the layer’s highlighted area, there won’t be any data to draw.