One of the (many) things that the SG-1 TV show handles poorly is making the Goa'uld believable as gods. This isn't surprising in many ways as to a modern audience the Goa'uld look like preening poseurs (again though the movie does a better job of making them look impressive), but to ancient Egyptians their divinity would have been obvious.
Imagine, it's 8000BC you're working in the fields living a very short life of grinding poverty and terrible diseases, with no access to running water and no literacy whatsoever. Your friends and neighbours die like flies whenever a disease sweeps through your rudimentary settlement, for there are barely towns let alone cities. Cats and many farm animals like cows haven't been domesticated, agriculture is in its infancy and there aren't any tools made out of metal.
Then one day there's a great shaking of the earth, lightning in the sky, and suddenly this vast, you don't know what it is, appears, floating downward. Most flee in terror, and in some ways they're the sensible ones, but some stay and see the ship open to reveal a gorgeously clothed figure, flawlessly clean, perhaps on a floating platform, wielding the power to hurl people away with a simple wave of their hands. What else could that orange glow be but divine power? Then there's the ability to heal the sick and even revive the dead, added to weather control technology and to a superstitious stone age human that is beyond magic, it's godly.
Over time perhaps that belief might have slipped a little, or maybe the people wh rebelled against Ra still genuinely believed him a god (his worship did continue after all) but could no longer suffer his brutal exactions. Resistance might have spread in the bureaucracies that the Goa'uld set up to govern the early humans, those becoming more educated through the system perhaps beginning to question their gods. Maybe the Goa'uld periodically wiped out any ruling elite, or seeded plagues which they miraculously cured to reinforce devotion to them.
Remember too that in Roman mythology which isn't so long ago in relative terms, it was accepted that gods could be injured and even killed, and that they weren't all-knowing. Even without these things, to a primitive mind the Goa'uld were still immensely powerful. If minds like Plato and Aristotle could accept such limitations in divine power then it's hardly surprising that they're accepted as gods (mostly) without question by the humans across a thousand worlds. It could be that many aren't genuine in their claimed belief, but know that open defiance leads only to death, a conviction which was broken when Earth rebelled, and when SG-1 first arrived on Abydos.
