The flexibility of Thatch is often seen as a much more versatile roofing material to use on roofs than more rigid slates & tiles. It will mould itself to any roof shape without the need for lead valleys and where there are changes in roof pitches.
These photographs illustrate this well.
We re-thatched this roof recently and the tiled roof is situated just across the road from it. I do not know if the tiled roof was once thatched?