A well made cheap knife can last someone for years. Maybe it's their favorite knife, maybe they don't like super expensive knives but would like to make the cheap knife they have a little nicer, it's all really personal preference. I want to put custom scales on my Spyderco Squeak($40) because I believe it will change the whole feel and look and make it just that much better. Why not make it your own(also better, more comfortable, or more desirable for yourself) if you are so inclined? I love my Spyderco Squeak and find it to be an amazing value, but if I put the Blue G-10/CF scales on it it will change the look and feel and be more desirable for me.
I'll be making it look, feel, and become, like an $80+ knife and that makes it worth it to me. It will be better and more comfortable for me.
It may not make a lot of sense, but if you really like a design and a knife overall, why not tweak it to better fit you?