Deep reality is a wild, scary place – scary enough that unless you have supernatural mojo on your side the unfiltered nature of reality will fuck you the fuck up.
Realising they needed safe havens – because whilst they might be able to survive in the Umbra themselves, their spouses, children, apprentices and other non-magic using loved ones and dependants couldn’t – the Traditions of Magecraft each created their own sub-world, populated by folk after their own heart. Each sub-world expresses only part of the whole of the true reality, and the selection of which part was based on the philosophical priorities of the Tradition in question.
The Technocracy was meant to provide the middle ground, their corner of the multiverse a place run not according to any higher spiritual philosophy but according to the cold logic of reductionist materialism. It was meant to be a place where those who did not wish to serve the Traditions could live and thrive, and where agents of the Traditions could meet in a place which lacked the dangers of deep reality but equally was not biased towards one Tradition or another. But what began as an experiment in seeing what humans could create without the aid of magic became a power trip. The Technocracy declared their universe the True Reality, and the sub-worlds of the various traditions heretical Deviant Realities. A brutal Ascension War began as the fragile peace collapsed. The Traditions refuse to swear allegiance to the Technocracy; the Technocracy claim that unless the Traditions set their philosophies aside and work together as a whole, they will not have the strength the face down the vast Nephandi conspiracy against reality.
Boom, I just solved two thirds of the problems with the basic Mage: the Ascension setting in one fell swoop.