Deep breath...shiny footprints....No Seriously, Welcome to BladeForums...
It's not only about cutting "cardboards". Here is an example, a bit broad but one I think will assist you in visualizing. Imagine a tool box, what do you see? Big screwdrivers, small screwdrivers, tape measure, small level, big pliers, small pliers, vice-grips, wire cutters, hammer, drill bits, wrenches (in yes, many sizes...

) etc... You have different tools for different needs. Sometimes a large fixed blade works for something, at other times a smaller folder is what is needed. It's about variety, some knifemakers consider thier craft a form of "art", if you can believe it - and we appreciate their craft, creativeness, and design ideas.
Let me ask you this - How many shirts do you own? Why do you have more than 1 shirt? Why do you have multi colored shirts that are in long and short sleeve? Why not just 1 single shirt? Are you then a fanboy because you own more than 1 shirt?
Clearly, you are missing the obvious, variety, collectablity, it's a hobby. Besides, my military can cut a slice of cake without getting my hands dirty...Can your little $10 sak do that? :foot: