The competition between Marvel and DC makes some degree of sense when it comes to comic books.
As popular as comic book movies are, they still come up far enough apart that most fans can likely find enough money to go see all of them, they don’t actually need to choose.
Even if you have a favorite character, it doesn’t mean you’re rooting for the others to fail.
As such, fans want both Captain America: Civil War and Suicide Squad to both be good.