What you're saying is very probably true of the US but this is a UK paper. Coke was not widely used in the UK until the 1990s/2000s. Ok, rockstars and people in the entertainment industry and the upper classes might have used it in the 70s/80s but it was not widely available, you'd have to make an effort or mix in rarefied circles to come across it.
With heroin, it was flooding into the UK and Ireland from the late 70s onwards in the wake of the Soviet invasion of Afghanistan, this is the background Bono was talking about with "Running to Standstill" and "Bad". Hundreds of people in working class estates in Dublin, who hitherto had at most maybe experimented with cannabis in terms of drug experience, tried heroin for the first time and quickly became addicted within a space of a few months in circa 78/79. Similarly in Glasgow and Aberdeen.
It's a geographical thing I guess, the US is much closer to the main sources for coke in South America whereas UK and Ireland would obviously be comparatively closer to Afghanistan.