Culture, and also despair. Perhaps similar to the US opiate crisis.
There are a lot of people in the UK who drink "too much", and a general distribution of people genetically predisposed to addiction. To drink yourself to death requires something more, usually falling off the edge of society. People who feel economically and socially unwanted, growing up in a "hard" culture.
Glasgow and Dundee in particular were cities of the Empire. When that came to an end in 1950 onwards there was a huge spike in unemployment, and a lot of the traditional heavy industries gradually left. This left a huge scar across both the physical infrastructure of Scotland (run down housing) and its culture. Trainspotting isn't exactly a documentary but it's a culturally appropriate portrait of how things were.
This is gradually changing as the country acquires 21st century industries (satellites, biosciences, video games, banking), but that on its own doesn't do a lot for the old drunks.
Just a note... Trainspotting was set mostly in Edinburgh, not Glasgow. Glasgow is worse off - it's a larger city that historically had a larger reliance on industry.
Rough stats... Glawgow's life expectancy is one of the lowest in the UK and lower than Edinburgh by 2+ years for both men and women. Its employment rate is nearly 10% lower than Edinburgh.
For Americans: comparing Glasgow to Edinburgh is a bit like Baltimore vs Washington DC. Not a perfect comparison, but close enough to get the general idea.
There are a lot of people in the UK who drink "too much", and a general distribution of people genetically predisposed to addiction. To drink yourself to death requires something more, usually falling off the edge of society. People who feel economically and socially unwanted, growing up in a "hard" culture.
Glasgow and Dundee in particular were cities of the Empire. When that came to an end in 1950 onwards there was a huge spike in unemployment, and a lot of the traditional heavy industries gradually left. This left a huge scar across both the physical infrastructure of Scotland (run down housing) and its culture. Trainspotting isn't exactly a documentary but it's a culturally appropriate portrait of how things were.
This is gradually changing as the country acquires 21st century industries (satellites, biosciences, video games, banking), but that on its own doesn't do a lot for the old drunks.