The DC Extended Universe (as it's unofficially become known) struggled from the start, and when it became clear to Warner Bros. that Zack Snyder's dark take on superheroes wasn't resonating with paying moviegoers, they went back to the drawing board. What followed was a Marvel-style makeover of this shared world that has, thus far, generated mixed results.
While things are slowly starting to look up for the DCEU, it's somewhat ironic that the R-Rated Joker was such a hit when Deadpool wannabe Harley Quinn: Birds of Prey crashed and burned at the box office.
The Marvel Cinematic Universe, on the other hand, continues to go from strength to strength. While current world events have postponed the Phase 4 slate, Avengers: Endgame's record-breaking performance (which saw it finally dethrone Avatar at the worldwide box office) makes it clear that it's a franchise which has found success in a way the DCEU simply has not.
With that in mind, why is it that the DCEU has failed to catch up to the MCU? This isn't about Marvel Vs. DC or deciding which fanbase you're part of; instead, it's all about some crucial mistakes Warner Bros. has made in the past which has ensured they'll never be real competition for Marvel Studios...