I first see about 80 cm high steps at both plots before the *ahem* "slight" slope begins. And yes, I would also strongly suspect that this could have to do with the soil conditions.
Even if it could be slightly removed to lower the plot to street level: this basin would then cause problems with surface water.
The price actually smells a bit like a pit and "the sewer is still to come," or similar jokes. A lot of money fits between "paved" and "developed."
And honestly, this looks to me like a "2000s DSL" village
Either way: for the extra earthworks, you can probably get a basement here as well.