A lot of it's just playing the odds. It's similar to big guys in football. Parcells used to call it the "world theory" when he coached the Jets. There's only so many guys in the world who are over 300 lbs, and athletic enough to play impact football. There are many many more guys at 240-250 lbs. So collecting the 300 lbs is very valuable.
Similarly, there are only so many guys out there who are 6-10 or taller who are relatively athletic, and can actually play. The dropoff comes quickly, and it's extreme. So the payoff in finding one is huge. Meanwhile, there's literally thousands of guys in the 6-5 to 6-7 range who can play a little. So finding one who's substantially better than the field is a lot harder. And the pay off is less, because the number two guy is still gonna be close.
Look at it like this, Gerald Wallace is something like the 40th best swingman in the league. Who's the 40th best big in the league? Now which match up is better: Gerald Wallace vs Kobe/Lebron/Wade, or 40th best big vs. Shaq/Duncan/Yao. Finding a good big is a huge advantage.