IT is an optical illusion
There is fuel in there
If you want to see the fuel filter full of fuel install it backwards to prevent getting an air bubble between the end of the filter housing and the open end of the outlet tube
Down side is all of the crud ends up on the inside of the paper so you can not see what has been dragged out
Some filters have no discharge tube so the end of the housing has a spiggot that you push the hose on that does not extend into the filter body .
While other the tube can go down as far as the very end of the element ( some actually support the paper element )