There's nothing there to route to, that's the point.
You're asking it to fill the area of the polygon with copper connected to a net. There are no pads or vias connected to that net in those areas, and the clearances disallow copper squeezing through gaps to get there, therefore there can be no copper there connected to the net. Nothing is unrouted, you have not performed a routing operation.
If you really, truly want a load of floating copper on your board to give you hell, feel free to tick 'Orphans'. You don't want that, though.