You say that like it's a bad thing. srsly, I just think they do it because multiverse crossovers are fun. Yeah, sure, it may well be a cliché, but it's one that WORKS. Although if you want to talk clichés, blame DC Comics and their constant universe-altering crises that they do every few years for no readily apparent reason. I mean, Crisis on Infinite Earths was fine, and they had their reasons for doing it, but nowadays they do it so damn often that it's blown all continuity out the window. Hypertime, Zero Hour, Final Crisis, Infinite Crisis, The Artist Formerly Known as Crisis, Flashpoint, Convergence, Flashvergence, Converpoint, 52, New 52...they never fucking stop doing those things. Now THAT is a cliché.