I'm just wondering if Galactus having had a dozen heralds maybe makes him look bad, because a lot of them have either turned on him or betrayed him. This happened with The Surfer, The Fallen One and Terrax, and Morg turned out to be bad. And Air Walker and Red Shift died pretty much right away. Only Stardust really seemed to work out and really have a connection and loyalty to (Maybe love?) the big G. His heralds don't seem to work out, but he keeps on making more. Can Galactus operate without a herald, and has he? I thought that there was a brief time when he did.
Depending on the story, he did not really need one early on. He hungered less often. One could argue that Galactus's tech and cosmic awareness should make the need for a herald moot.
And that should be right, but the initial idea was sort of the herald as an angel of sorts coming to fortell the wrath of God and it stuck on.