Why don't construction prices go down?

Here is some information from Bavaria, after I made my decision: My offers (from three different companies) ranged from 2600 €/sqm to 3200 € with high-quality equipment. Everywhere included earthworks, KFW40, heat pump, controlled residential ventilation, everywhere parquet flooring, lift-and-slide doors, etc. The latter with wood/aluminum windows, carpenter interior doors and a few small details.

I would go for the one with the wood-aluminum windows and the carpenter doors!

For a 160 sqm house, that's a bargain surcharge of about 100k compared to the cheap offer. You didn't calculate, did you?

Yes, even slightly above. In the end, we significantly upgraded the cheapest of the three offers, but overall stayed below €3000/sqm.

Congratulations! And a rough confirmation of the always mentioned +/- 3,000€

Yes, however, I would describe the equipment as significantly above standard. With plastic windows and CPL-coated doors, etc., it would have started at €2600, as mentioned. Without controlled residential ventilation, electrical and network gadgets, or at a lower KFW standard, significantly under €2500 would have been possible.