To illustrate what I mean, here is an example (even though not from the single-family house sector)
Schwiemu owns a multi-family house with an attached commercial building (residential and usable area probably 1500m²-2000m²) with an estimated 10,000m² of land in a valley location by a stream. The property has several ponds, trees on a steep slope, outbuildings, etc. In summer, it is a totally idyllic location.
But just to keep the property somewhat in shape, you could employ someone full-time. I don’t even want to talk about the buildings. The money you put into renovating it, you will never get back when selling.
If you wanted to sell the place, it would probably only go to a nature lover with a big wallet for personal use as a summer residence. But there aren’t many of those.
The same house with a "reasonable" plot without ponds and outbuildings might instead attract a completely different buyer group as an investment property and thus achieve more.
What I want to say is, no matter what ratio is given by the building authority, if you deviate too much from the local norm, be it plot size up or down or house size up or down, then the property becomes a niche object and prices go down. But I don’t see that with the order of magnitude mentioned by Marvinius.
With houses under 80m², it would probably be different. There, the calculation by buyers (with rising land prices and increasing space requirements) in 20 years would rather be land value minus demolition costs.