My family on one side came here with nothing at the turn of the 20th century because this was the best place to be, they embraced being British, fully integrated into British culture and my great grandfather and grandfather fought for those British values in both World Wars.
Heritage and culture is important, whatever nation you come from. These are our roots they mean something.
Your entitled to your opinion, nihilistic as it sounds.
But your grandfather and great grandfather lived in a very different world. One of near constant conflict and competition between countries within Europe, this re-enforced national identities. You, however, live in a post nationalist world where conflict and competition between neighbouring countries is now largely played out in sporting arenas. Beyond that there is very little driving force to maintain and reinforce national identities. This is where Brexit comes in. It's been a reactionary attempt to turn back the clock to a time of conflict and competition. To recreate the world as it was fifty years ago. Or some imagined, idealised view of it.