That's interesting - I wonder where you are? Our ca. 1800 cottage has no foundation (it's literally just rocks sitting on dirt) and is in a pretty wet climate (Ireland). Though the room that had a screed put down is drier than the others.
Go farther South and it gets down to eventually nothing. Go far enough North, to permafrost country, and you not only need to dig down to the permafrost but you need to have insulation so the permafrost doesn't melt.