Without actually investigating first hand, I can only conjecture. But my guess is that the players are all set up with a certain radius of dim light. Each player is only seeing their own dim light (i.e. the light emitted by characters they directly control). The DM is seeing the combined light of all light-emitting tokens, since they control everything. Dynamic Lighting doesn't actually light anything. Think of it as a black mask over the map, that each character can reveal independently. Most characters with darkvision or torches will have where the mask is partially made transparent (dim light), or completely made transparent (bright light). The GM is seeing a view with all of these overlapping "revealed" areas, and thus seeing the map with very little masking of darkness. Thus the map will appear brightest to them. Another possibility is that the player view is displaying areas revealed by Advanced Fog of War, but have no current light source. They will only see areas they have already seen, and in dimmer gray scale. Again, the GM is not confined to AFoW masking and sees the map at full brightness. Without direct investigation, and given the washed out Player view image, it's impossible to tell which of these, if either, is the case.
