I wouldn't go so far as to say wasted... using ethernet cable good is because it's a cheap and readily available source of some light guage wire. And if you have solid core wire instead of stranded wire, it is also a perfect source of wire suitable for breadboards.... so those unsed pairs might just have a use as well! 
btw, stranded wire is more flexible than equivalent solid core wire, is also a better conductor, and suffers from metal fatigue (breaking due to frequent bending) less, hence why more cables are using it. Doesn't stop them from being a PITA in comparision to their solid core counterparts when wiring your own othernet cables! 
btw, stranded wire is more flexible than equivalent solid core wire, is also a better conductor, and suffers from metal fatigue (breaking due to frequent bending) less, hence why more cables are using it. Doesn't stop them from being a PITA in comparision to their solid core counterparts when wiring your own othernet cables!