These leaks keep appearing since many years but their origin is not necessarily a hack of the government infrastructure. The leaks usually occur at election cycles because the address based electorate data is handled and processed by the political parties(which are not exactly IT elites) and gets stolen or leaked.
Then there were high profile hacks of large food delivery services or other e-trade platforms.
All this resulted in people collecting and merging data from multiple leaks and re-selling those.
Edit: At some point, all the lawyers were using this data to track down people relevant to their court cases. They were selling it in CD format back then. Scammers and other criminals probably use this data too.