Why were the believers in Jerusalem so poor in the book of Acts?

Les explains that the poverty of the Jerusalem saints grew out of the events recorded in Acts 2, 3, and 4. Because they sold their goods expecting the King to come, they would not need them; when the King was rejected and did not come, they were naturally left destitute. God providentially provided for them through the offerings of Paul’s Gentile converts. Les notes that Romans 15 and 1 Corinthians 16 designated those offerings for the poor saints in Jerusalem. Returning to Galatians 2:9–10, he points out that James, Peter, and John, who seemed to be pillars, gave Paul and Barnabas the right hands of fellowship: Paul and Barnabas would go to the heathen/Gentiles, while they would go to the circumcision/Jew. The only added condition was that Paul should remember the poor—the saints in Jerusalem—which Paul says they were forward to do. In Acts 15, Les also notes that Peter came to Paul’s defense at the Jerusalem conference, and God in His sovereignty sees the big picture, even using Peter’s earlier experience at the house of Cornelius to prepare him for that later defense.