Thanos didn't know.
In this Multiverse, with the Main Universe at its center, the Celestials put immense pressure on the Dimension Lords.
As long as the Celestials kept a firm grip on the Main Universe, the Dimension Lords had no chance of turning the tables.
The Celestials could find them and come to kill them at any moment.
It was this enormous outside pressure that kept the Dimension Lords so united.
Without the threat of the Celestials, they would probably have beaten each other's brains out by now.
That made it easy to understand why Satan worked to preserve the appearance of peace among them.
And it wasn't just Satan. The surrounding Dimension Lords felt the same way.
After all, no one who reached Universal Level or became the ruler of a dimension was a fool.
In the end, Thanos decided not to defy Satan. He had his Avatar leave behind half its body and handed it over.
Seeing Thanos yield, Satan didn't press him further. He and the other Dimension Lords welcomed Thanos, then explained the rules of the Quantum Realm.
They weren't allowed to kill one another or take things by force, and all the lords shared responsibility for upholding promises made before them.
There weren't many rules, but they maintained a surface peace among the strongest beings in this Multiverse.
Afterward, Thanos began asking around about the Multiverse.
Perhaps because he had behaved reasonably earlier, the Dimension Lords didn't shut him out. They soon told him things that weren't secret.
For instance, none of the Hell Lords would submit to another, but Satan was still their leader in general.
Chthon and Dormammu were master and disciple, though lately that relationship was on the verge of reversing.
There were also stories of who had explored the Chaos Ruins