The reason why Hawking failed to enter the first echelon of physics is that he still has a certain gap compared with masters such as Yang Zhenning and Einstein. Among the top in the physics world, Newton, Einstein and Maxwell are firmly in the top three, and no one can shake their position. followed by Dirac, Yang Zhenning and others. Some people have compared Hawking to Yang Zhenning, which is obviously an exaggeration. 
However, despite the fact that Hawking's theories were mathematically flawless, none of his theories during his lifetime were empirically proven. Even if all these theories were verified to be correct, he failed to open up a new theoretical framework in physics, let alone move towards the road of great unification. 
In contrast, other masters such as Dirac and Yatlin have made seminal contributions in the field of physics. Dirac fused quantum mechanics and special relativity, Yatlin unified the three fundamental forces, and Boole is known as the father of quantum. These masters are all powerful and groundbreaking beings. 
To sum up, despite Hawking's outstanding contributions to the field of physics, his achievements are still inferior to those of the masters of the first echelon. As a result, he failed to rank among the top of physics.