Many of the countries that remain in and strongly support the EU are likely to, in the immediate term, not give excellent trade terms to Britain to keep the perceived cost of leaving high to avoid encouraging leave movements in a couple of other members.

And then it's a poker game. How much are they willing to hurt their already lethargic economies to punish the UK? I reckon if all countries has a referendum, a fair few would vote to leave as well. It can't sit that well with people to punish the UK for leaving when there's a sizeable number of French, Dutch, etc, who want to leave as well.

Doing a deal which is positive for the UK will mean threatening the integrity of the EU (and all the potential economic chaos which could go with it).