Compared to, Captain America: Civil War, which built on all 12 of the films that preceded it in the franchise, Scott Derrickson’s movie is much more focused on its titular hero’s corner of the world, and as such doesn’t make any time for big cameos or namedrops.
Doctor Strange is absolutely part of the larger Marvel Cinematic Universe, featuring a number of elements that tie back to other movies and characters, but overall very much exists as its own thing.
Given the fun that comes with the interconnected-ness of the MCU, some fans may question why we didn’t see more of it in the magic-fueled blockbuster – but the explanation is rather simple: there just wasn’t space to fit it into the story that needed to be told.