Thats because only idiots and magazine journalists (who get forced by said idiots) try to just rank cameras ? All cameras have strengths and disadvantages. You cant just rate that on some scale and then declare one best. The question is what you want to do. And for most people its also a question of budget.
The D810 is the current image quality flagship. It can do anything, but its definitely the top choice for landscape, portrait, and studio. It doesnt have much in respect to fps though, so not such a great sports camera.
The D5 is the current reporter and sports photography flagship. Extreme reserves to get the picture, no matter how awful the light and how fast and irregular the subject moves. Also build to last. Interestingly so much optimized for low light that its performance in good light is somewhat underwhelming.
The D500 is the current top camera for wildlife photography. Also endless lowlight reserves. Its basically a D5 with a crop sensor.
The D750 is the current allrounder full frame option. Compact and lightweight and a flipscreen. Better lowlight performance than the D810, but cant touch D5 (and the D500 is in some areas better in lowlight, too, not to mention in respect to autofocus in low light).
The D610 is the current cheap entry into full frame.
The D7200 is the current semiprofessional crop camera. Its basically the lowest end for professionals, because it has sufficient controls to not keep menusurfing during operation. The D500 is better in most respects, but also a lot more expensive. The D7200 is more optimized for general image quality than lowlight.
The D5500 is the current higher tier entry level camera. It lacks many essential features for a professional photographer, such as sufficient controls to operate the camera quickly, an in camera body autofocus motor for older lenses (prefix AF instead of AF-S), or more advanced flash features.
The D3400 is the brand new lower tier entry level camera. Its basically optimized for being cheap. Its still a very competent camera, just like the D5500. You'll have a very hard time to distinguish a well made picture from the D3400 with a picture from the image quality flagship D810. Still the D810 has more reserves, is much better build, operates much faster etc.