Why does Zeus rule over more than his two brothers do?

After the war with the Titans (the Titanomachy) the three brothers, Zeus, Poseidon, and Hades, divided the realms between themselves by lot. Poseidon got the sea, Hades the underworld, Zeus the sky. It should be noted that the realm of Zeus included the the surface of the Earth. As man dwells on the surface of the Earth Zeus had a lot to do with them and consequently there are more legends about Zeus than the other two. And as there are sailor on the sea Poseidon has more legends than Hades does. Hades was not a neglected God however, he was given authority everything in the earth including all ores and stone so he had a lot of respect from miners and masons and the like.

Now to the really ancient Greeks the sky wasn't all that much of a realm. It was considered to be a dome that held the stars and rain water, not really a super great place to have, so the surface of the earth was thrown in as well to make Zeus's realm more equal to the other two.

Now Zeus was able to bully the other Olympians rather easily but with his two brothers he was more conciliatory. Zeus and Poseidon argued over the possession of a certain sea nymph and (with a little intervention from Prometheus) Zeus relented to let Poseidon have her. When Hades kidnapped (and possibly raped) Persephone, all the Olympians asked Zeus to rescue her but Zeus could do no better than to secure a poor compromise. "Unlike every other offspring of an Olympian pairing of deities, Persephone has no stable position at Olympus."