It was because it took a lot of time to recover from the destruction of facilities by fire (in November 1869) at the planned site of Mint Bureau which was to produce new currencies, and to clean up fake money and inconvertible paper currencies circulating in the market.
新貨幣生産を担うべき造幣局予定地の火災（明治2年11月）による設備の焼失や、市場に流通する偽金・不換紙幣の整理に時間を割かれたためである。