Yeah, it might be a non competitive investment for private investors because of the high risk compared to the low return or because the benefits are only seen y

Yeah, it might be a non competitive investment for private investors because of the high risk compared to the low return or because the benefits are only seen years down the line, so results in a low annualized rate (you need to do it via nth root, not via dividing the returns by n). So governments do that investment instead. As a government you see things differently. Unless it goes abroad, the money is never gone, but is just going circles in your economy. If there is an added benefit of improvements decades down the line, even better.