I live in Edinburgh, and 100 year old buildings are the newest ones in the city. A good chunk of the city is what we call a “conservation area” - so you can’t modify the aesthetic of the building (windows included), but the vast vast vast majority of people outside that space have double glazed windows I’d wager.

Windows have a lifetime of only 15-30 years, though. If you have to replace them anyway, you might as well get double-pane (even if the rest of the house isn't well insulated).

Also in australia, the BCC/NCA is an absolute joke compared to basically every other industrialized country. There’s a reason for the annual “Austrlian houses dont meet WHO minimum standards” articles.

As an example single pane windows havent been effective or widely used since the 70-80s in north america and europe. And both places energy standards effectively preclude them since 2000ish. Or insulation in australia is effectively absent in pre 2000s, and maybe R-4ish on a new build now. Conversely NA was R-4 in the 70-80s and it would be about R-6 (or more) these days.

Our residential solar and heat pump uptake is great. But for building standards and quality were a joke.