Why all of the middle-weight so called great boxing fighter of the era are fearing from GGG?

To beat GGG - you have to know what GGG is (boxing style-wise). GGG is (at heart) an advanced crowder. A crowder is a boxer who cuts the ring, takes your space away, and applies pressure before unleashing combinations. The feet of the crowder are not as dynamic as the feet of a swarmer (a cousin to the crowder), but the crowder is more scientific as a result (they need additional techniques to get inside and to gain angles).

The problem is also that GGG has an extensive amateur background and has picked up some outside boxing tricks (a hard jab and outside lateral movement - which he showed against Lemieux).

The styles that give the crowders problems are 1. The Brawler (especially someone that has a granite chin and one-punch KO power and swings for the fences without moving around) 2. The Boxer-Puncher (They keep the crowder/swarmer on the outside with multiple jabs and foot spacing {or they can tie up & wrestle} and then unleash outside power combinations when the crowder/swarmer tries to get in. A perfect example is the fight between Kell Brook {boxer-puncher} vs. Shawn Porter {swarmer}).

Because GGG is an A-level advanced crowder, you need advanced Brawlers or A-level boxer-punchers at Middleweight to beat him. At present, those do not exist. The closest thing is Andrade down at Jr. Middleweight and DeGale up at SuperMiddlweight, but I think GGG beats them both as they are now...

Triple G is a great fighter with devastating power. He would stop anyone in his division. It would take a master boxer like Ward to beat him. And unfortunately no one at middleweight have skills like SOG.

Because he's 34-0 with 31 KO's.

He hits hard and is skilled.