There could be 100 reasons, it is more likely to be a combination of factors.
Asians usually have a lower lung capacity than white people who have a lower capacity than black people.
Most BAME people in Britain are a result of mass migration from the 19602 and 1970s, immigrants usually move to cities and the BAME populations still live in cities. People who's ancestors arrived in Britain 200 years ago are often still found in cities.
Lots of cultural factors, one (of many) reasons type II diabetes is badly controlled in some communities is due to beliefs about food. Things like the amount of sugar believed to be in vegetables depending on whether it is grown under or over ground.
Living conditions / traditions may play a part, culturally white British people are used to the idea of a care homes for elderly people, other cultures are more likely to keep granny in the family home .
When my Nana became a widow (30+ years ago) her neighbours who were mainly Pakistani couldn't understand why she wanted to live alone when she had three sons.
Then there is DNA, northern Europeans may have developed a gene that gives some protection. Most of the world is lactose intolerant, but most white people are not.
Some populations cannot tolerate alcohol.
The village of Eyam in Derbyshire has a population today with a higher number of people with a genetic immunity to the plague than the general population.
So take your pick, of course it could also be non of those things.