Why the ground wire on Icecap ballast?

[HDAlien]

Just installed a fixture from Marine Depot with 3 Icecap 400W ballasts, the wiring harness has three ground wires coming out of the harness, why aren't the fixtures grounded internally since they use three prong plugs? Where are those ground wires typically grounded? I'm trying to get a cleaner install without having to ground in the outlet itself.

[Aquaduck]

For safety reasons, the ground from the line cord needs to connect three things.

1. The ballast case.
2. The metal enclosure the ballast is mounted in.
3. The reflector the lamps are mounted in.

Anything less is a safety hazzard.