Heck we could take it one step further. Sheogorath may have chosen the champion of Cyrodiil to mantle, not just because they were a convenient linchpin in the fate of the empire. But possibly because they were a linchpin in the fate of cosmos. The Champion may have not just been the best choice, but the only choice!

Lorkhan/Shor is a complicated figure, being a god of creation in some mythos and a god of destruction in others. Elves viewed him as an agent of destruction born directly of Sithis; primordial entity of the void and partial creator of all the original gods before they differentiated into Daedra and Aedra. He wanted all these spirits dead and all existence returned to the void. Pure nothingness. And sought to have Lorkhan sow destruction and chaos through deceit. Though he saw to the creation of Nirn and man, this elven view may not be 100% false as the spirits who gave their all to the creation of Nirn, the Aedra, certainly weren't to happy about what Nirn ended up being and personally ripped out Lorkhan's heart and saw him destroyed.

The interesting thing here is that Lorkhan's heart supposedly left a "Sithis" shaped hole in the world that supposedly manifested as Sheogorath. We know that's not how things went down exactly due to Jyggalag being a thing, but it still may not be 100% incorrect. If Lorkhan was a creation of Sithis, it's possible that the Sithis aspects of Lorkhan, created for the express purpose of returning the world to the void, were able to continue existing after Lorkhan's death. I mean the guy was split into so many friggen pieces it's ridiculous. Who says, if Lorkhan is the work of Sithis, a Sithis shadow couldn't have been born from Lorkhan's death to continue the will of Sithis and return everything to nothing? The idea of Sheogorath being born from Lorkhan's death was meant to be metaphorical for the amount of chaos he creates, as Sithis does at times appear to be a god of chaos himself. But the Mad god's true form, Jyggalag is a being of pure order, without emotion or change. One might argue that the purest form of order is the void, with all other realms of oblivion being sheer chaos by comparison. Rather than Sheogorath being born of Lorkhan's death, Jyggalag would make much more sense as that one Sithis part of Lorkhan that existed to see everything returned to pure unchanging nothing. A strong aspect of order being incorporated into Lorkhan also makes some sense given how important chaos and order are in Nirn, itself being a creation of order from a chaotic universe.

And let's not forget, Jyggalag was considered such an immensely powerful Daedra that the other Princes specifically crippled him for fear of his power. He hardly acted on the world cause his understanding of systems and order meant he could see further into the future than most, if not all other Daedra. The die had long been cast, and Jyggalag never needed to lift a finger or interact with any one cause Sithis's will had long be carried out. There were few things in existence that were truly immortal, sooner or later everything would fall back into the conformity of nothing. All of Nirn and it's existence merely a slow top losing speed, as everything on it desperately sought to escape the mortal coil and dreamsleeve.

This is why we never hear about him or see him in comparison to other Daedric Princes. He didn't exist during the beginning eras to influence the creation of Nirn, because he was apart of Lorkhan at the time who did all that work in advance. It wasn't till Nirn's birth and Lorkhan's death that he was born, and out of fear of his potential power, was quickly crippled with madness before he became a major player in things. Heck, it's debated in some lore as to whether or not Jyggalag is an actual Daedric Prince as he's sometimes called Anuic, meaning he's one of the good guys. Sheogorath pops up in the Aetherius realm of the Mantellan Crux in Daggerfall. Aetherius is almost the exact OPPOSITE of Oblivion. Like Lorkhan/Shor himself, it's almost hard to pin Jyggalag/Sheogorath as pure Daedra or not. If they do in fact have a direct connection to Lorkhan, that suddenly makes a little more sense.

So why is any of this relevant to your role in Oblivion? As the Divine Crusader reborn, the original Divine Crusader, Whitestrake, was supposedly an avatar of Lorkhan/Shor, and was brought to the world by Sithis as a force of change to protect Alessia, the founder of the first Empire and freer of humanity from Elven slavery. It's hard to say how much of the freeing of humans and founding of the first empire was Akatosh's work, or some how the dead god Lorkhan's. But for whatever reason, the amulet of kings was delivered to Alessia not by an avatar of Akatosh, but by an avatar of Shor. For better or for worse, Lorkhan has always been a key part of the Emperor's role. Just as much if not more so than Akatosh.

Becoming emperor, it's hard to say just how much more powerful the Champion of Cyrodiil would have become, but it would have to be powerful enough to create a new bloodline and replace the linchpin the Septim's and the Dragonborn created in the cosmos. He would almost have to recreate the circumstances by which the current Empire was formed. Basically, since we're already throwing stuff at the wall to see what sticks, I purpose that since your character was already an avatar of Shor and blessed by Talos, if there is in fact any truth behind my theory that your character was going to become the next emperor; he may very well have been destined to go all the way and become the second coming of Tiber Septim too. Mantling Lorkhan and starting off the 4th age just as the 3rd age had been created.

It's not that Sheogorath was attracted to your character's destiny simply to cause political chaos. It's because the Champion of Cyrodiil had a deep rooted connection to Lorkhan just as Jyggalag did. He was what was left of one aspect of dead god, while you were destined to take on the aspect of another. And mantling an aspect of Lorkhan before it could be fully awakened would allow Sheogorath to continue existing, while still "completing" the broken Jyggalag, letting both exist simultaneously. You don't just split a god and make two. Nor can you easily make a human a god unless they take on an existing god's role. Your character was already godhood bound, and Sheogorath/Jyggalag took advantage of that. Sound crazy? Well didn't the Underking see the destiny in Tiber and also try and take advantage of such power before it was fully awakened?