Euro zone: Why is the effect of low interest rates modest?

Interest rates have been very low in the euro zone since 2014 , and they: Have led to a limited upturn in corporate investment; Have not prevented the European equity market from remaining undervalued. How can these modest effects of low interest rates in the euro zone be explained? Possible explanations are: Investors or companies do not believe yield curves; they believe long-term interest rates will rise sharply; The fact that the required return on corporate capital has remained markedly higher than long-term interest rates limits the effect of the fall in interest rates on investment. If the effectiveness of the expansionary monetary policy is modest in the euro zone, then the policy mix between monetary policy and fiscal policies must probably be rebalanced.