For one, it is wary of unnecessarily stoking investment in riskier things, like loans to high-risk borrowers or excessive investment in real estate (if interest rates are very low, investors are more likely to seek out higher returns in riskier investments). In a similar vein, it doesn’t want inflation to go too high, too quickly. Additionally, the Fed has to essentially reload on interest rate ammunition so that when the economy weakens again, it has the ability to decrease interest rates and give the economy a boost.