Reunification meant that Germany's power in the EU increased. Becoming a bigger country with a larger population got more seats and pushed the bloc more in its direction. Thus reducing Britain's influence there.
Also noteworthy, the Soviet Union dissolved shortly after, at the end of 1991.
Whereas Germans, East and West alike, had largely thought of themselves as Germans in varying senses since Bismark (and both the DDR and BRD claimed to be legitimate successors to the same historical state), the peoples who lived (and live) in Northern Ireland didn't all think of themselves in the same way. Some thought of themselves as British, some as Irish, and many as some mix of both. A big reason why historians mark the Good Friday Agreement as the end of The Troubles is that it recognized the right of each person in Northern Ireland to identify with the nationality they chose (self-determination), in a way that both the British and Irish governments cooperated to recognize in administrative affairs where nationality mattered.
There wasn't a separate ethnoreligious East German identity. There were (and are) conflicting identities in Northern Ireland with ethnic, religious, national, and historical dimensions. The two situations on-the-ground were extremely different.