Why don't construction prices go down?

Because it is only cut once (untermass), and not sliced into 4m pieces,

And my question is, why do you cut off almost a whole decimeter when cutting, and that is supposed to be okay? You don’t have to inch your way to some measurement bit by bit. If you have a tolerance of +/- a few centimeters, you just have to avoid cutting roughly wrong once. I have also cut stones. That your method is the less error-prone option is true, but that’s not the question.

Why is he planning it then?

The windows were ordered according to the factory plan and are installed...

The carpenter was there to check the doors... they fit as well

Plan the kitchen according to the rough construction dimensions in the plan? Excuse me? Measure up when the interior plaster is applied, anything else is sheer madness?

You can make a fuss, but no one will rebuild the wall for you, that's how it is. Maybe there will be a little money as compensation.

If you have +/- a few cm tolerance, you just have to avoid cutting very badly once. I have also cut stones before.

If a team of masons builds a shell in 40 hours, there is no time to keep cutting, not to mention the botched, overlap dimensions, and crumbled stone corners.

So, is the limiting wall offset, meaning is there more space on the other side? What you can definitely demand from my perspective are the (additional) costs for adjusting the kitchen. If the 9 cm are completely missing (along the entire length of the house), you are also entitled to compensation for the smaller usable area. However, I would only bring this up in the final payment, otherwise they simply won't continue building.

So is the bounding wall offset, meaning is there more space on the other side?
What you can definitely demand in my opinion are the (additional) costs for adapting the kitchen. (...).

Can you try, the statement will be that you only take measurements for a kitchen once the shell construction is completed or the interior plaster is applied. Including the interior plaster, there is already an allowable tolerance of 2.6 cm.
Anyone who plans and orders a kitchen exactly to size with this in mind cannot be helped.