Showrunner Marc Guggenheim has explained why the Arowverse couldn't cross over with the DCEU before Crisis on Infinite Earths. Earlier this year, DC fans got an unexpected treat when the DCEU's Flash (played by Ezra Miller) met face to face with the DC TV version of the fastest man alive (Grant Gustin) during the Crisis crossover. Their exchange was brief yet memorable, with Miller bringing much of the same gee-whiz charm that made his Barry Allen a standout in the debacle that was 2017's Justice League movie.
As it turned out, Miller's Crisis on Infinite Earths cameo was not only a last-minute addition, it was actually incorporated at Warner Bros.' request. This came as a surprise, considering the studio has resisted crossing the streams when it comes to their DCEU movies and Arrowverse TV series in the past, sometimes even forcing the latter to abandon plotlines (like their version of the Suicide Squad) to avoid competing with the DC features. According to Guggenheim, the key to changing things was simply time, patience, and having new bosses to report to.
Speaking on the Fake Nerd Podcast, Guggenheim talked about the challenges of getting access to the DCEU, and what led to Miller's Crisis on Infinite Earths appearance becoming a reality:
There were certain things that we knew were not touchable and the cinematic universe fell into that category. The nice thing about doing something for eight years is you're there for all the changes. You're there for the personnel changes, and you're there for the philosophical changes and the changes in policy, and this just happened to be one of those situations where people changed their minds. I was so glad that they did, even though the change of mind did come after we were wrapped on the whole crossover. So it came very late, but as they say, better late than never.
I did feel like the cinematic universe was the one that got away, if you were to ask me - short of bringing Christopher Reeve back to life - what would you most want to do? I would have said include the cinematic universe. I still can’t believe that we were able to do that.
The funny thing is, once we got the approval, it came together almost easier than any other cameo. I mean, certainly, there were cameos that were a lot harder to pull off, that required a lot more scheduling creativity or financial creativity or logistical creativity, you name it! This sort of all came together really nice. It was a series of phone calls and some time at the keyboard writing a scene and bing, bang, boom, we just got it done.
Indeed, the DCEU has seen some sweeping changes since Justice League disappointed: Walter Hamada, who helped transform The Conjuring into a successful shared universe, took over as the President of DC Films in 2018 and the franchise at large gave up on trying to copy the MCU's interconnected storytelling in favor of making standalone films that are loosely part of the same continuity. Because of that, Warner Bros. finally came to see the benefit in having Miller and Gustin's Flashes (briefly) team up in Crisis - both as a way of pleasing fans who've been wanting to see the pair together for years, and as a bit of cross-promotion for The Flash solo movie they've scheduled for Summer 2022 (with Miller starring and IT's Andy Muschietti directing).
Of course, it helps that Miller was able to firmly leave his mark on his Justice League role in the first place, and people have been calling for the character to return to the DCEU ever since. There's been no indication of similar DC crossovers happening in the future just yet, but with Crisis ending with a whole new multiverse being formed (one where other non-Arrowverse TV series and DC movies still exist on separate versions of earth), the door remains very much open for future crossovers between DC's superheroes from the big and small screen alike.
Source: Fake Nerd Podcast
