Not everyone needs a high capacity diaper. If you're very active and only need a low capacity, or are only wearing a diaper for the padding and not the absorbency, thinner might be better. (and probably cheaper too)
I have to wear somewhat tight-fitting pants to work, and preschool plastic are right on the edge of "ball-crushing" for me. I wish I could wear Simple but they're too thick and too wide for me to wear comfortably during my workday.
For me I want as stimulating as possible while still being comfortable. Once it stops being comfortable, it stops being fun, and then there's just no point to it at all.
I actually find the new Waddlers to be more comfortable, higher capacity, and more durable for daytime wear, but they're a good deal more expensive and not staying in stock enough for me to be able to depend on, so for now I'm sticking with Preschool Plastic. Waddlers are a great alternative though for people that want space-grade capacity in a thinner, velcro tabbed, or high-swell diaper.