A: He did not want to limit how much money he could raise for his campaign.
The decision to opt out of the federal presidential campaign financing plan allowed Barack Obama's campaign to raise unlimited amounts of money from individual donors and organizations. By choosing to forego public financing, Obama was able to raise and spend more money than he would have been able to under the limits of the federal financing plan. This gave his campaign a significant financial advantage, allowing him to run a more competitive campaign.