This is essentially down to the mainland forgetting that Northern Ireland existed until Brexit forced the NI border issue to prominence, isn't it?

The UK is to a great extent a set of special cases that have accreted from the feudal era. No wonder we invented Mornington Crescent.

All of the compatibility issues and awkwardnesses that derive from this get glossed over as much as possible, but are starting to force their way to the surface as the power and competence vaccuum in the center loses its grip.