Electrician question: grounding a ballast for retrofit light installation

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I installed two 48" Sunlight Supply T5 retrofit light kits in my 75g plant tank and I am in the middle of installing another Sunlight Supply 36" retrofit T5 kit in my 58g plant tank.

The 48" retrofit instructions clearly showed that the ballast should not be grounded.

The 36" retrofit kit did not come with any instructions but the ballast has no ground wire attached where the spot is to put a ground wire in.

Clearly these folks don't want people to ground their ballast.

I am wondering why? Isn't it an electrical hazard to leave the ballast ungrounded? There must be some reason they do this; they are a well-established company with a reputation for quality.

Anyone who knows more than I do about electrical stuff care to comment?