The purpose of the change was to allow for the creation of more SBD to hinder "pump" attempts that raise SBD beyond it's intended peg value of $1 USD. But it's important to note that the increase in potential SBD doesn't risk the sovereign debt problem that the US has: the STEEM blockchain is designed to linearly stop honoring the ability to convert the SBD to Steem at the rate of $1 worth of Steem when the debt ratio goes above 10%. Think of it like a built-in promise of the Steem blockchain to hyper-inflate SBD's value vs Steem during the period that "too much" SBD is in circulation.