I'm not sure that was the main reason, as, despite pfm not, with hindsight, being a microcosm of the country's feelings (
), it looks like having been a leadership clash (chalk and cheese here), most people being absolutely fed up with the indecision about Brexit and the realisation (which surprised me) of the economic nonsense of Corbyn's manifesto. The Global markets were awaiting certainty to invest and the E.U. wanted Boris to succeed.
Blair's Labour party was not only different at inception but contained some eminent people, esp. in financial matters. It was a far cry from the very left- leaning and anachronistic policies of Corbyn.