In the US, comics are considered by the masses to be the bane of pubescent boys or puerile adults obsessed with superheros and cosplay.
In France, graphic books (they're not all novels) are an elevated and widely-used cultural resource. They're found in educated bookstores, museum shops, libraries, and basically everywhere. And you know what? They're terrific!
France (and Belgium) have access to wonderful historical series on every period you can name. Tons of biographies of famous, real people. And beautiful, illustrated tomes which they can use to spark their imagination and learning.
It would be more accurate to say that Americans aren't spending money on graphically illustrated books because that's not an accepted part of our culture here, rather than to try to slam the French for something cool that works well for them.
See also: Scott's McCloud's Reinventing Comics [0] and BDfugue [1], a terrific online store for bandes dessinées.