My wild guess: it's easy-ish to drill a hole into the hilt and expand it into an oval.
It's then much harder to then fit some plastic housing inside the hilt, such that wires are hidden, but with the exposed crystal chamber having enough room.
I'm not familiar with other designs, but I'd think you'd also want some light to pass through the crystal, so now you're adding more LEDs (probably on both sides), and woompf, you've just upped the complexity.
So it's a bit like saying: why not add a lot of acceleration capability to a Toyota Camry? You could... but then it's not really a family sedan, it's a souped-up Audi. Leave the lower-priced family sedans to Toyota, and if you need glamour and acceleration, go spend the big bucks on an Audi.
Note: I am (obviously) not a car person, so my car analogy may suck, but hopefully it sufficies.
Also, I'm not saying this is a bad idea. On the contrary, I totally bet Ultrasabers is constantly thinking of ways to do this -- only inexpensively.
