Hunts, built in wait time.

[JustPlainLucas]

Okay, time to explain it as if I had to a monkey.
You see a $10 note on the floor, you pick it up. No one else can pick it up because you have.
You find a B rank hunt, you start to kill it. Others could also take part and earn seals even though you are killing it currently.
One copy of the money in your analogy exists. Multiple "copies" of Seals exist for everyone that takes part.

I pick up the 10 dollar bill. No one sees me pick it up, so no one knows I took it. While this is happening, a bunch of people found a box of 10 dollar bills in an alleyway down the street, and are sharing the bills to all who arrived. My point, I honestly don't think anyone freaking cares that I took a 10 dollar bill and didn't share it.