Pretty sure that's objectively false. Superman sells more merchandise than almost anyone. Bats, Spidey, and the Avengers as a collective group move more, and that's it. And all of them have the benefit of popular and successful live-action adaptations in the recent past to help them.
The fact that Superman sells as much as he does, even after decades of being mismanaged in comics and larger media, shows just how much people love him. Hell, we're basically born knowing who he is, and it seems to me that (for most people) the natural default is to love Superman and the concept of Superman. People turn out for his stuff.....it's only after everyone sees that the product is lackluster that they lose interest. It's like that quote from Nelson Mandela, “No one is born hating another person because of the color of his skin, or his background, or his religion. People must learn to hate, and if they can learn to hate, they can be taught to love, for love comes more naturally to the human heart than its opposite.” No one is born hating Superman. They learn to hate Superman after seeing WB screw him up over and over again.
The LCS crowd might think Clark is out-dated and uncool. Everybody else is a different matter. Give people a decent film with the kind of Superman they expect to see, and it'll do just fine. If Aquaman and Captain Marvel can break a billion, Superman could shatter it easily.....if WB could only figure out the character and make a worthwhile movie with GA appeal.