My guess is Manfred deadened the ball so that hitters stop swinging for the fences as much and shift their approach. The issue is that pitchers are so good now that even making contact is difficult, whether it's in the air or otherwise. With how bad this season has been in terms of offense, they will almost certainly start incorporating those experimental rule changes because long term this is not good for the sport.
Although I am glad that the deadened baseball, if nothing else, has hurt the hitters who hit cheapo HR's. Unfortunately that list includes Biggio so it hurts the Jays, but at least it makes the HR a bit more an accomplishment.