I don't think they need worship. They existed before humans did per Ethniu so that wouldn't really work. They're elementals, beings representative of primal forces. Like Dragons, they need no direct worship. Only continued knowledge by humanity of their existence. Or to put it another way, the things they embody are part of reality, of existence to humanity, ergo they can't 'unbelieve' them. Unlike the Queen's, who have taken the power upon themselves, but do not necessarily represent it in it's entirety. Man's the winter queen, not the queen of the artic and antarctic. Per recent Woj the queen's are mostly northern hemisphere, relying on liaisons with the southern wild fae. Where as the frost Giants were probably winter in it's totality.
I don't know. On one hand, the oldest generation (Ethniu's dad) might have been angels/Aspects/Avatars that don't require worship or humans; they just exist(ed) with their own power tied to their nature.
But the Eye of Balor ran off terror and fear. Maybe papa Balor could fuel it on his own without help, but Ethniu needed the boost of fear to charge it.
Seems likely that each generation lost a bit of their Powered by their Nature fuel and grew more dependent on Human Interaction fuel.
That fits with the Hecatoncheires being Titan-spawn and them being able to make armor from Mordite. They are kind of half of the Outside half of the Material, then the later Titan-Spawn (what we call Gods) became more tied down to the physical world. I think Dragons come from the middle layer. They are lesser than Angels but greater than most of the Gods.
It seems likely that the eldest generation predated reality, and time, and are therefore beyond the limitations of those born within both.
Uriel, the Fallen, and the Walkers might be the only ones we've seen in the series that fit the bill for that. Everybody else is a few to many generations down the line, up to and including wizards as very diluted progeny.