It's a perceived wisdom and I have been known to swallow it. French music, and especially pop/rock, may suit a domestic audience but does not easily appeal to the ears of Anglo-Saxons (as the French like to call us). Indeed, there are plenty of French people who would sooner listen to American or British pop and rock.
But recent developments have prompted me to rethink the theory. It may have a little to do with my neighbour Jean-Louis, who plays guitar in a way I'd love to emulate but never will; I could gaze at his lead guitar runs all night. Come to think of it, I already have gazed at them for much of the night. It has more to do with a relatively new phenomenon, French artists making a point of singing in English.