I think this might be to cope with a collar bone injury. These were perhaps more common when horses were the normal form of transport.
I broke mine in a motorcycle accident and, common to most people with this injury, the ends knitted out of line, mainly because it can not be splinted.
This has given me a pronounced knob just inboard of my shoulder pocket which doesn't like guns recoiling against it. I know this because, even though I normally shoot from the other shoulder, part of my BASC coach training involved shooting off the 'wrong' shoulder.
A slim heel to the stock would have avoided the knob and removed the tendency to seat the butt more towards my shoulder muscle and upper arm.
The wider toe would imply a thin chest with little in the way of pectoral musculature, probably a more common feature in a time of rampant TB and relatively poor nutrition in the rural population.
Or it might just have been widened to spread the recoil load. After all, a narrow toe is more about tradition than necessity providing the toe has more cast outwards than the heel.
We tend to imagine the shoulder pocket with the arm hanging down while in fact when shooting most peoples trigger arm is lifted to about 40-60 deg. This opens out the bottom of the shoulder pocket, easily accommodating a wide toe.