Why don't construction prices go down?

Oops, your footprint is by virtue of sperm lottery higher than that of the majority of Africans.
Anyone born into a society entirely based on fossil energy does not change the entire society with their individual demand.

I recommend googling the "tragedy of the commons." The social scientific description of a phenomenon that has just taken hold of you. Quote: "The tragedy of the commons arises when each farmer tries to let as much livestock as possible graze on the common pasture for as long as possible and no one takes care of the soil. As a consequence, the land eventually becomes barren and the livestock starve. According to Hardin, the tragedy lies in the inevitability of this catastrophe, which emerges from the collective behavior of supposedly rational individuals, namely those acting in their own self-interest."

(...) Even as a homeless person in a European city, you cannot not (double negative on purpose) rely on petroleum-based products. Suddenly, your footprint is by default higher than that of the majority of Africans. (...)

What specific guilt do I bear for the "Spermalottery"?

But the truth is that many countries in southern regions don’t even have our problems regarding insulation and heating...

Yes. But do you want to buy/build with a provider who offers ruinous prices, meaning around break-even or below cost? For a mass product that I receive and then pay for, okay. But for a house, where I might still report significant defects and rely on them?

We had that during the pandemic when everything stood still and our competitors, out of desperation, started offering prices below cost. That’s when we got out of the downward spiral at the latest. Two of those are now insolvent or have been bought out and "restructured."

In this respect. The downward spiral in prices, which is now slowly starting to turn. That doesn’t necessarily have to be good for the customer. Many will be left by the wayside and unfinished houses will remain.

PS:
I did build with Town & Country, but I never had the impression that they were close to bankruptcy, even though they are really affordable. If they suddenly cut prices by 20% for the same house now. Where is the saving supposed to come from? It can only be at the expense of quality.

Or is that just the impression the company leaves because they offer better prices?