Kimouette, try to envision how a pegged mortise and tenon joint holds the timbers in position and transfers force, in multiple directions, while the timbers are seasoning ie shrinking, twisting and checking. Then envision timbers essentially butted and toed by screws, with the screws set in a fixed position as entry and exit points, what will happen as the drying timbers fastener contact points change position? Will there be riving and compression failure at the contact points? Also screws are a poor substitute for bolts and bolts are accompanied with washers, plates and gussets.