People in the Young Stone Age (Neolithic) did not “almost exclusively” built their houses on lake shores. All thinkable sites were used:
Plains, hillsides, mountains, creek and riverbanks, fens, islands, at lakesides, in lakes, borders of woods, open sites in woods etc.
However, the circumstances of conservation for prehistoric house ruins are not the same in all places. Large parts of floors, walls or roof constructions only remain conserved when without oxygen, meaning at best in the mud of lakes or swamps, because in those cases, Stone Age houses were for the larger part made of wood. In other settlement areas this is different. Here, post holes or garbage pits which are very difficult to recognise are the only witness of the buildings which once were. This is the reason, why well preserved debris of prehistoric houses in most cases are to be found at lakesides, in lakes or in swamps. However, as said before, this does not mean that people back then built their houses “almost exclusively” on lake shores.