One unique aspect of Northern Ireland (among many others) is that the region has never really had its own independent identity. The population is politically aligned with the UK and culturally with a mix of UK and the rest of Ireland, leaning more towards the latter. Irish sporting teams for example all include Northern Ireland as well, making the whole situation even more bizaree. This makes it very different from the other countries it is being compared to in that article (Scotland, Wales). It follows that there was never any need or desire for an official flag.