Disney/Fox Merger: 8 Disastrous Implications It Has For The MCU
4. There's No Way To Alter The Lore
The actual logistics of implementing the X-Men into the MCU are anything if not difficult, owed in part to the fact Marvel Studios already came up with an explanation for Scarlet Witch and Quicksilver.
In the comics, Wanda and Pietro are the daughter and son of Erik Lehnsherr - the master of magnetism himself - Magneto. They're mutants, much like their father, but with them both having had stints as Avengers, Marvel were well within their rights to use them in the MCU, sans the mutant backstory. The in-house explanation, per se, is that the twins were given their powers by Baron Strucker's personal infinity gem.
It fits the universe nicely, even if the original comics explanation is a fan-favourite. The problem with introducing mutants, then, lies in the way Marvel have built their world. It wouldn't make sense for homo superior to exist within the MCU because we'd have heard about them already, and while a spontaneous event like the Terrigen Mists (the comics event that created new Inhumans in 2015), could work much the same for mutants, it would feel at odds with the wider connotions that surround the X-Men in the first place.
Put simply, it gives Marvel a headache they don't need, and a cast of characters they wouldn't know what to do with in the first place.