Reading this article one thing shocked me: Do a lot of homes not have double glazing in the UK? I thought it was a standard, because it's so much more efficient at keeping cool/warmth inside/outside (depending on season)
That said there are a lot of a) old buildings that are protected and so can't have the windows replaced easily/in an economically viable way (e.g. each window needing to be hand-crafted in wood to non-standard sizes to look identical bto what was there before), b) a lot of just properties nrented out to single people who rent a single room etc and the landlord simply doesn't care/bother, c) houses that were lived in by someone for the last 30/40/50 years where basically no maintenance or decoration had been done - they've died and someone else had moved in.
All the previous homes I lived in had mould fungus growth on walls and behind wall papers. The double glazing ensured air-tight house but lack of air circulation. Single glazed windows seem to be really good at preventing mould growth, of course at the extra cost of heating bills.