for the record I love both characters and read both titles, but when it comes to Superman/Clark's popularity, I feel like his popularity takes a hit because of his other media. The comics portray Clark as a complex character and he's had a lot of great arcs and fun stuff from Golden to present. The tv series and movies from the 70s and 80s is where he takes a hit because they decide to paint him as a human or alien AMERICAN FLAG!! TRUTH JUSTICE AND THE AMERICAN WAY!, so they decided to turn on the cheese to Mach 25 levels. Clark in the movies is painted as this bumbling dork and his entire motivation for saving humanity is Lois. That's it. And he's so much more than that. So because of that perception, no wonder people find him a boring character who flies and has powers and is un relatable. Meanwhile, Batman and his family rise in popularity because a) he's human and b) he kicks ass with his fighting skills and has a kick ass costume. And now with the recent films, Superman can't even get a sequel by himself, he has to paired with Batman.