> And what prevents greedy people from forming Bitcoin to remove (or increase) the maximum coin count and getting enough other geeedy miners to go along with it to be the majority fork?

The nodes define what a bitcoin is. So long as they agree that bitcoin should follow the original exponentially decreasing reward schedule, then that is what will happen.

There are some problems, for instance, if almost all miners decided to switch to another fork, then the original chain would simply die because of the difficulty. But miners have electricity bills to pay and are strongly incentivised to mine the most profitable chain. It is not a matter of convincing the miners, but of convincing the world that your uncapped fork is more valuable.