It's only been five years since Christopher Nolan concluded his trilogy of Batman movies with The Dark Knight Rises, but a lot has changed in the superhero movie landscape since then. The Marvel Cinematic Universe is bigger than ever, DC has formed its own cinematic universe, 20th Century Fox has expanded its X-Men world, the list goes on. Regardless, in Nolan's opinion, the Dark Knight trilogy had the luxury of being spread out over many years, whereas superhero movies these days, as well as many blockbusters based on popular properties, are being rushed out. As Nolan put it:
That's a privilege and a luxury that filmmakers aren't afforded anymore. I think it was the last time that anyone was able to say to a studio, 'I might do another one, but it will be four years'. There's too much pressure on release schedules to let people do that now but creatively it's a huge advantage. We had the privilege and advantage to develop as people and as storytellers and then bring the family back together.
Batman Begins was released in 2005, seven years after the Batman film series came to a grinding halt with the critically-derided Batman & Robin. The Dark Knight followed in 2008, and The Dark Knight Rises wrapped things up in 2012. Usually the standard wait time between two connected movies that aren't filming back-to-back is two to three years, so for Warner Bros to be so cool with Christopher Nolan waiting longer to put out The Dark Knight Rises was bold. Of course, it undoubtedly helped that in between The Dark Knight and The Dark Knight Rises, Nolan was making Inception. Even though Batman was on hiatus, at least the studio was still benefitting off Nolan's creative mind. In any case, as Nolan commented at a BAFTA: A Life In Pictures event (via Deadline), he appreciated having more time to work on his Batman saga and better realize his vision for the DC Comics superhero.
Nowadays with the current superhero movie model, the leading studios are churning out them out left and right, and rarely are they willing to delay these movies (particularly sequels) for a significant amount of time should an obstacle or two arise. And when it comes to these cinematic universes, even if a specific character doesn't have a standalone movie coming for a few years, they can still appear in other stories. For instance, it did take four years for another Thor movie to come out after The Dark World, but the God of Thunder starred in Avengers: Age of Ultron and cameoed in Doctor Strange during that interim period. And going back to DC, in a little over a year and a half, Ben Affleck has played Batman just as many times as Christian Bale did. It's gotten to a point now where Marvel, Warner Bros and Fox are churning out two-three superhero movies per year, which keep fan appetites satisfied to a degree. But on the other side of the proverbial coin, Nolan makes a good point that the rush to release these major motion pictures can sometimes impede the creative process.