I'm very confused on why Ebberon's cosmology doesn't match the one seen in the DM's guide. Is the DM's guide only talking about Toril's cosmology, and all the other material planes have their own cosmology? I will greatly aprreciate all who respond.

I am not very familiar with Ebberon, being mostly familiar with Forgotten Realms, but from my understanding, yes, the cosmology in the DMG is mostly about Toril. While in some ways, all the settings are part of the same multiverse, some of the settings operate differently: different afterlives, different gods, planes, etc. Again, I don't know much about Ebberon, so someone who is more knowledgeable may be able to fill in the gaps, but from my understanding, it's a pretty different world from FR, and I have heard that it operates on a fairly separate cosmology, too. 

Thank you for your replies!

Quote from Lyxen >>

The "Cosmic Wheel" cosmology was created with AD&D for Greyhawk and has been the standard cosmology for D&D Worlds which did not have their own specific one, including the FR (it's slightly different from Greyhawk but the principles are the same). By the way, I love that one, it's really the basis for Planescape, which is really one of my favourite settings ever.

Eberron, on the other hand, has a very specific and distinct cosmology to support the links between a number of entities. It's also not completely clear because of some of the principles of Eberron design to keep players on their toes and to leave options for the DM.

So yes, don't apply what is in the DMG to Eberron. There is a specific chapter in the Eberron Sourcebook about Planes of Existence, which says: Eberron is part of the Great Wheel of the multiverse, as described in the Player’s Handbook and the Dungeon Master’s Guide. At the same time, it is fundamentally apart from the rest of the Great Wheel, sealed off from the other planes even while it’s encircled by its own wheeling cosmology. Eberron’s unique station in the multiverse is an important aspect of the world: its planes have profound and shifting influences on the Material Plane, and it is sheltered from the influences and machinations of gods and other powers elsewhere on the Great Wheel.

 The last paragraph of your response pretty much sums up my views on Eberron.

The DM's guide is talking about the Forgotten Realms cosmology (ie Toril).

You are correct in that the other material planes generally have their own cosmology.

If you want more information about Eberron's in particular, the Exploring Eberron book that Keith Baker published in July is available on DM's Guild and each plane has a couple pages dedicated to it.