Superman just suffers from poor media products i.e. nothing kids can truly enjoy; movie, TV, or cartoon. They did do Justice League Action, which was shortlived. They really do a disservice to Superman as a whole, honestly, and I'm not even his biggest fan. Sometimes I think they just need to go back to basics for kids with Superman - he's strong and saves everyone. Done.
Even the toys suck. They follow the MoS movie colours, and so to a kid they probably look dead compared to Captain America and co. Just look at the toys on a shelf, the Superman toys that follow the movie colour tone look awful and boring. Even compared to Batman, and that guy wears black and grey, yet he looks cool on a shelf! They need to go back to classic Superman, using the lighter blue - navy New-52 blue at max, but not the MoS colours. Shifting a moment to the adult market, MAFEX released Batman and Superman based on the Hush comic. Superman looks awesome! Kids need more of that sort of look.
Anyway, the fact is Disney are killing it with the way they handle their properties and merch right now. Warner is struggling even there for everything else that isn't Batman - they introduce lots of new lines that get canned quickly from poor pickup. From what I heard, there tended to be a real lack of interest from retailers in DC property, especially Superman (all based on MoS look, FYI).
That said, LEGO does give DC a boost where their other media may not perform as strongly, so there's that. But I doubt that performs all that strong either. Would love to know.