I think that's because SW and Marvel are so important to Disney, they can be scheduled and rescheduled for whatever reason and everyone else on those dates will clear out of their way. They can afford the time to make things right since the competition will defer to those two franchises.
Also, if you're familiar with the history of Hollywood. you'd know it's not unusual or new for them to depend on sequels, remakes etc. There are so many series of movies that they've produced over the years to mine every last dollar out of an idea, character or property. For example, think of all of the Charlie Chan, Thin Man, Andy Hardy and Sherlock Holmes films they made or all the B-westerns with stars like Roy Rogers and Gene Autry. These were series that had a built-in audience that kept them alive for many years. I think the difference then is these less-expensive pictures were used to beef up profits which would be reinvested to make A-list films, whereas nowadays the A-films are the series films and studios live or die depending on the success of these tentpole films.