Why has the ECB never succeeded in lifting expected inflation?

Despite a highly expansionary monetary policy since 2014-2015, expected inflation in the euro zone, as measured by inflation swaps, is no higher today than in 2014. It did rise from 2016 to mid-2018, but then fell markedly . Why has the ECB not succeeded in lifting expected inflation? Neo-Fisherism offers a first possible explanation: a long period of low nominal interest rates leads in the medium term to a fall in expected inflation; A second explanation is that the situation of banks has deteriorated: flat yield curves and banking regulations have reduced bank s’ profitability, leading to weak credit supply and ultimately rendering the expansionary monetary policy ineffective. Faced with this observation, will the ECB persist with its low interest rate policy?