Because the idea that Shavers was the greatest punchers ever at HW comes largely from guys who beat him. Guys who took his best shots and were not KTFO such as ali and holmes. Those guys were actually knocked down and or hurt or KTFO and beaten by other fighters. Why does holmes not call Tyson who actually knocked him out the hardest punchers he ever fought? Because its it can be too painful, too wounding to a fighters pride to give the guy that beat you.
Fighters like to give credit to guys that gave them a hard time yet who the ultimately conquered. It's like an old war story they can use to pumped themselves up. Shavers is just a feel good war story.
Yeah, that's simply not true.
"Shavers. No question. At least with Foreman I was able to get up. When Shavers hit me I went down and stayed down." - Ken Norton when asked who hit harder
"Lyle hit about the same as Foreman. Shavers hit harder than Lyle and Foreman put together." - Leroy Caldwell
"Oooh man, that man is always with me. He hit so hard, the hardest. I still feel his punches today." - Jimmy Young on Shavers
Each of these three guys fought both Shavers and Foreman and each of them were stopped early by Shavers as well, with two of those guys being stopped early by Foreman. Both Norton and Caldwell express a clear advantage for Shavers in the power department as well with their quotes. Guys like Jimmy Ellis, Joe Bugner, and some others who Shavers stopped are also on record saying he hit them the hardest out of all their opponents. James Tillis went the distance with both Shavers and Tyson while being knocked down by both, and he always maintained Shavers hit him harder of the two. Sure, there are fighters like Ali, Holmes, and Lyle who did beat Shavers and maintain he hit them the hardest out of anybody. But there's more than a few who will admit the same after having been knocked out by him
If you watch the Lyle-Shavers fight and watch the punch Shavers hit him with at the end of the 2nd round (or was it 3rd?), are you really going to disagree with this quote from Lyle?
"Shavers hit me so hard it felt like needles were jabbing the back of my head. Without hesitation, Shavers was the hardest puncher I met." - Ron Lyle on Shavers
Lyle may have came back to win that fight against Shavers while also having lost to Foreman. But sorry. There's no way Foreman hit him with a more powerful punch than the left hook that Shavers almost knocked Lyle dead with. There's no way.