You have to realize that people have limited money. Of course the best way to go would have been to buy the house, insulate the roof, the walls, change all windows and the heating at the same time.

But we can't afford that. So we start with the point that saves us the most money, is mandated by the government and subsidized by 50%.

At this point, we have costs for heating of about 1500€ a year. Upgraded roof insulation could bring that down to 1000, but would cost approx. 30k so it would pay for itself in 60 years at current prices, at that time I am 97. Walls have a similar ROI, Windows are worse.

Well insulate the roof when we redo the tiles, we'll insulate the walls when we renew the paint,... And when we are done with that, we probably approach end of life of the heat pump anyway.

Oh, and by the way, energy efficiency class C(after renos) or D (before the renos) is nowhere near as bad as you claim it is.