If the pool grows at the same rate as the academics who need money from the pool, it's zero-sum. If the pool were ever to grow more slowly, then it's a negative-sum game. That's when all hell breaks loose -- by many accounts, this is unfolding now.
In other words, the academics do not grow the pool through their own actions, as in private business. They are forever reliant on the kindness of strangers.
That's not quite right. Academics do grow the pool through public outreach and demonstrating value to companies which lobby the government to fund them, but since there is usually one big pool (such as the NSF budget), it is impossible for people to grow their own pool directly. It's closer to working at a large company, where your impact on earnings is next to nonexistent and your career is determined by the beliefs of the people around you about your impacts on them.
Negative sum is the worst outcome. Only the cheaters win in that scenario and they slowly eat the legitimate players, then the weak cheats so only the biggest cheaters remain. The entire pool is then tainted.
We have acquired a couple such companies and the people that survived that environment are some of the most toxic players you ever meet. They are also really good at the game so they immediately rise to power and begin to devour their next victim.
In other words, the academics do not grow the pool through their own actions, as in private business. They are forever reliant on the kindness of strangers.