Labour’s individual policies, particularly the left-leaning ones, were highly popular. Support for public ownership of the UK’s water, gas and railway companies sat at around 70-80% nationwide. More than 60% of the electorate also supported increasing taxes on high earner’s. 
The fact that these policies on their own polled well would indicate that it wasn't the content of the manifesto that was unpalatable to voters, but perhaps the messenger itself. Corbyn was a highly divisive figure and lacked the charisma and charm to win the game of personality politics that a strong election performance requires.