Why did the early disciples stay in Jerusalem?
They stayed in Jerusalem to present the offer of the King and the Kingdom to the nation of Israel, hoping Israel would accept their King so Christ could return and set up the Kingdom. The Twelve did not leave, while other believers were scattered.
Les explains that the early disciples, specifically the Twelve, were not going to leave Jerusalem, but all the rest of the believers had. They were to stay and present this to the nation of Israel, in hopes that Israel would still accept their King, and Christ could have come and set up the Kingdom. They understood that once they had the King and the Kingdom, they knew the Old Testament prophecies, such as Zechariah chapter 8, where ten men of all nations take hold of the skirt of a Jew and say, "We'll go with you," because they know God is with you in the person of the King.