If you remove all the capitalists maintaining the system, communism will naturally win because it’s how humans naturally think.

So why then did that system not last forever? Why did capitalists emerge in the first place? Drag is treating them like some kind of external force, as if they were aliens dropped into societies across the globe.

The material conditions of what Marx called primitive communism naturally caused society to develop into the hierarchical structures of early civilization. The development of agriculture created incentives for the division of labor, for states with static borders and organized defenses, and for class structure and involuntary servitude. In a hunter-gatherer society, it's far more efficient to treat everyone (mostly) equally, because either they're going off on their own to hunt or forage or they're coordinating with a group and need to be armed and trusted - but this is no longer the case with agriculture. The people who responded to these (unfortunate) incentives were able to become dominant.

It doesn't actually matter that much how humans "naturally think." If you put a bunch of robots or aliens or whatever into a situation where there's an incentive to do something, then provided they have the ability to innovate, experiment, and try new things, someone will eventually discover the incentive and reap the benefits of it and others will follow, either because they see the benefits or because the benefits strengthen the beneficiaries to the point that they can force everyone else to go along with it.

This whole idea of, "Well Marx said indigenous people were communists so it's trivial to just get rid of the capitalists and go back to that," makes it very clear that Drag hasn't actually read Marx and is just proof-texting, picking out random bits and pieces to support Drag's pre-existing beliefs without actually understanding anything he said. A communist society in the modern day, with technology and capital, would look drastically different from hunter-gatherer societies. There are aspects of hunter-gatherer societies which we can point to as worthy of emulation, but we can't return to a hunter-gatherer economic system (or lack thereof) without the mass starvation of the vast majority of humanity.