A backlit keyboard only lights the legends if the keycaps are built to let light through. Many sets are not, and that is a deliberate choice rather than a defect.
Three behaviours
Opaque sets block the light entirely; you get glow around the cap, not through the legend. Front-printed legends sit on the front face and light up toward you. Side-printed legends light from the side of the cap.
Reading a product page
Every set on DeskeyX states its shine-through type in the spec table. If it says opaque, the legends will not light — no matter how bright the board is.