Why shouldn't they ? Because any half decent (or better) individual or group would be more than willing not to implement (nor threaten to implement) an unnecessary action that may well cause violent conflict. It's about morality and not threatening folk in order to get your own way.
The EU has a habit of taking court action (in the ECJ, natch) against its members. Nice club, really, that takes its members to court. And still it goes on:
I wondered that last night but couldn't be bothered to ask.
I would have thought that f a neighbouring country had lent Ireland money (which they'd have to have borrowed and which their taxpayers were paying to service) then Ireland would have been less disposed to imposing border controls on that country (especially when there is a specific bilateral agreement not to do so). Still, it's a funny old world.