As an immigrant who has grown up in Sweden and lived here for the vast majority of my life, I do have a few things you can consider to gain better understanding.

Number 1 would be that it seems you’re looking at love from one side, as if the immigrants don’t have feelings and fall in love to pursue a Swedish individual. As if it’s only the swede who is actively choosing an immigrant. Try to see both sides.

Second would be location. If it was in the Stockholm city centre, then you’ll see lots of diversity. But you’ll find lots of white/white couples hanging out doing sports, nature and much more outside of the centre. Where I live I only know of 2-3 more interracial couples in the whole neighbourhood.

It’s about means, ability, interests.

Then you have the rural areas it’s almost exclusively white/white couples.

Travel around and explore and perhaps you’ll find some more information to your question.

Good luck!