Supply and demand as Agent has stated.
Most normal users don't use their laptops in dark rooms or use them with the lights on in the room so they can see the keyboard. I bet most of these would complain if an additonal 20-30 pounds was added to the cost of their laptops just so the keyboards can be back-lit.
You could get some USB LED lights to illuminate the area needed, or thinking even further out of the box use a LED based head-light that you see for camping to light the keys when you look down