RE: why
Hm. That's an interesting question. I still have my Whitetail Hunter, and got it when I was like, 12 I think. Anyway, your post started me thinking about how that bow shot. Back in those days, the heavier the arrow the better. I remember shooting 45 pounds, and my arrow was a 29 inch 2018! Can you believe that? Also, the bow itself is like 45 inches long, or something like that. So, my conclusion is that a properly tuned bow didn't matter as much, because the ATA was huge, and the arrow was only flying like 170 fps.
Conversely, now a days we have short ATA bows, lightweight, carbon arrows, and all the other bells and whistles, making everything that much more important.