At the risk of being an armchair psychologist, I think the reaction to Trump's tax changes is understandable - it is seen as him overcoming challenges after a long battle, and a harbinger of him doing so in some of the promises he made they see as personally advantageous. If you like, they see it as reaffirming the vote they made in the first place.

I predict disappointment to come.

We could get a similar effect here. To date, there is nothing that has happened to give the Leavers the same boost. But if the EU, for example, were to concede to no payments, we would see the same. In the meantime the Leavers have to live on "we won, get over it".