Filling them with fuel would do nothing. They would just all run multiple out laps to the grid on super rich mixtures to burn it off before the start. As Brundle said, no team will ever start a race with an ounce more fuel than they need.
F1 has always been about saving something. Tyres, brakes, gearboxes, engines, etc. F1 has never been a flat out sprint. Ever.
Indeed, it's always been there but we have way more team radio and onscreen graphics now showing it. If you took these away again, it would be how people think it should be again.