Not a stupid question at all! This method works for several reasons:
Typical soil contains the majority of nutrients in the topsoil layer, which is roughly 1-10in (2.5-25cm) deep. Because compost is added up to 2ft (60cm) deep, roots will grow much deeper to take advantage of the easily accessible nutrients.
When the soil is kept loose, plants can grow roots through it much easier; French intensive gardening focuses on loosening the soil very deeply and avoids compacting it so plants don’t have to expend as much energy pushing their roots through hard soil.
As a result of plants growing roots deeper rather than wider, they’re able to be planted much more densely and grow more produce than market gardening in the same size plot!
Not a stupid question at all! This method works for several reasons: