Support for Brexit is down to less than 40%

For those interested in more detail see Peter Kellner's piece in the Guardian The polls are clear: support for staying in the EU has rocketed

There is a campaign amongst the (predominantly remain supporting) youth to turn out the vote next time. Many who were too young to vote in 2016 are now eligible. By the time of another vote, there will have been about 1.2 million deaths in the UK, mostly older people and I assume biased to 'leave'.

Independent of Kellner's survey, and without anyone changing their mind, there is likely to be a narrow majority for remain next time. That in itself would explain the reluctance to have a vote; a narrow swing to remain could be thought to be more unstabling than the status quo.