When you think about it, a 301, being a straight stitcher, has a lot less internal mechanism to move than a 401 does. The 401 has the internal cam stack, the parts to swing the needle bar.
I'm not sure the weight of the 401, but it is definitely heavier than the 301's 16-17#. The 401 may have a more powerful motor than the 301, but I would guess the majority of that extra power goes to move the extra internal mechanisms. Speed is sacrificed somewhat to accomplish zig zag.