Mostly just for geographical reasons, no? If you have a free travel area covering a large swathe of continental Europe then it's inevitably going to include mostly EU member states. AFAIK there has never been any substantial objection to Ireland and (formerly) the UK opting out of Schengen, which obviously wouldn't make sense for those countries given where they're located.
Mostly just for geographical reasons, no? If you have a free travel area covering a large swathe of continental Europe then it's inevitably going to include mostly EU member states. AFAIK there has never been any substantial objection to Ireland and (formerly) the UK opting out of Schengen, which obviously wouldn't make sense for those countries given where they're located.