Crisis on Infinite Earths featured brief nods to the DC Universe shows, but those were seemingly made up of stock footage instead of actual cameos filmed for the crossover event. As it turns out, there's a very good reason for that as the likes of Titans and Doom Patrol were made under the proviso that they wouldnt be forced to tie into what's happening on The CW.
During an interview with Fake Nerd Podcast, the Arrowverse executive producer explained that those DC Comics adaptations were made with an "expectation that they would never have to participate in The CW crossover." He went so far as to say that "creative assurances" were made to those involved with them, including producers and, believe it or not, the actors starring in them.
"[This] is an Arrowverse event, it’s done on the Arrowverse shows, and when we were breaking the story, we were always trying to find the right balance between, ‘OK, well, how many non-Arrowverse characters should we bring into this,'" he added.
Of course, we've heard from those who do participate in the crossovers that they're not much fun to film due to the manic production schedules, while Smallville alum Michael Rosenbaum refused to appear as Lex Luthor due to not being given a script (and being offered a woeful amount of money).
Guggenheim went on to explain that it would also be tricky having Arrowverse characters be "co-opted by characters that, quite frankly, viewers who don’t watch those other shows wouldn’t know and understand." So, despite them all being on the small screen at the same time, it was clearly too complicated finding a way to bring them all together in an event like Crisis.
However, it's hard not to wonder what this is going to mean for Stargirl...