It technically DID happen with all the proxies, North Stars, HABIT and Rake and stuff, forming an almost slenderverse mcu, (I liked Everymanhybrid, mainly because the motherfucker playing HABIT was visibly having the time of his life, but it started to get much more urban fantasy, less cosmic horror, in the later installments.), but those could be easily ignored if you so chose and mainly existed because they wanted stuff to happen while Slenderman was chilling in the background, they didn't have nearly as much of an overbearing presence like all the autistic sublevels, entities, and researchers currently do on the Backrooms. It's just such a different landscape, these days, where simplicity and the unknown aren't as welcome as they used to be.