Yep, factor caused by a divisive campaign to water it all down.
Should just have said "we're off" and forced them to negotiate with us instead of trying to pussyfoot round all the various issues, instead at every turn there has been whining, disunity and opposition to everything our side of the negotiation has said.
Had they offered proper concessions to Cameron when he went asking for them before the referendum, we wouldn't be here, yet we have pandered to them over and over again.
They manage open EU/non-EU borders in Switzerland, Norway etc. It's not impossible to do, if you are willing to do it.
This area for you to discuss any other topics