I will keep it as real as I can. Cuts are similar to the way old baseball cards were traded. The better cuts you have and the rarer they are, the better chance you have of obtaining a cut you want. The bad thing about this is that it becomes an addiction really fast. I had over 60 strains, I lost all but one, now I'm back up to ten strains and I told myself I would just stick to three or four.
People horde cuts for several reasons.
It takes hard work to make and find an elite cut. Sometimes this takes years. Then someone comes along and crosses your cut with another strain touting it as their own. A lot of people are guilty of this and it's not always a bad thing, but I'm sure it hurts the person who made the original cut.
Someone takes your cut and crosses it not knowing what they are doing and watering down the potency, molesting and tarnishing the original cuts name.
Sometimes it's just business. Growing the same strain creates competition and lowers the price. Having the same cut in another region does not affect the price but it can if the cut is really good and spreads all over every region. The same goes for seed vendors, they want to have elite moms that other seed vendors don't have.
Sometimes it's out of respect, when people ask you to keep a cut on lock, you do it. The cannabis community in my area is small and everyone pretty much knows each other. You don't want a bad rep, you'll get beat down literally in this scene.
Sometimes it's just for bragging rights......my dick is bigger than yours!