There are no welds on the frame itself...
You have the left and right sides of the frames as single piece objects, which both lowers the cost and removes weak points (welds) from the design. Switching from steel to aluminum means the frame is now lighter as well.
The engine is also a stressed member, so the frame being bolted at the tripple-clamp is not a weakpoint, as the left and right sides are actually joined at several places through the engine.
You have the left and right sides of the frames as single piece objects, which both lowers the cost and removes weak points (welds) from the design. Switching from steel to aluminum means the frame is now lighter as well.
The engine is also a stressed member, so the frame being bolted at the tripple-clamp is not a weakpoint, as the left and right sides are actually joined at several places through the engine.