This! It's like reading Marvel Comics. You don't sit there being like "Man. It just doesn't make sense that the avengers don't help Spidey stop Doc Ock this time." You read them being excited over the crossovers you get, that make sense in the given story. If everyone was constantly crossing over, it would make it less special. That being said, I feel like the resolution of Infitiny Wars would be a good time to do it. It wouldn't take much to show quick clips of SHIELD or The Defenders while showing earth.