Humans literally created social structures to stop those very same kinds of abuses, I'm not allowed to go to my neighbor's house and tell him he has to sell me his computer or I'm going to burn his house down, so why do we let nation states behave in this manner?
(fwiw I've thought of this too, others have as well, that very fact should indicate our rationality leads us to better behavior than this garbage)
No larger body of greater power exists to regulate the behavior of states credibly. Law of the jungle consequently re-emerges.
Sometimes one state is of sufficiently greater power than two others and is able to perform that role. The big boys, though, no, there is no organization capable of it.
We've not yet created a social structure of that overwhelming scale. Nor do we seem close to it. The attempts are toothless and suffer from a lack of buy in.
As for competition like the hypothetical of you vs your neighbor, yeah, we did set up a social structure that prohibits those kind of direct plays. In practice though, I'm not sure how much different sending your kid to a fancy college is. It's an attempt to establish greater access to resources, which, in a limited resource environment, is itself competitive. It also carries a weighty opportunity cost in that you've spent what probably amounts to a fairly high % of your resources on something meant to benefit kin, ignoring the opportunity cost of using those same resources towards altruism which would be of far greater benefit to a far greater number of people.
We do cooperate, of course, within a framework that actually still supports really extensive competition with disastrous consequences both socially and environmentally(2nd larger in importance as time goes on). It's who we are.
TBH I'm not sure the moral consensus against violent plays on the individual level came first. Some elite benefits from the labor of the loser and is therefore incentivized to prohibit that sorta direct move. I think that may have actually been the real reason for its existence, with religious frameworks later arising to justify it, but on this point, I'm not particularly sure.
Should automation really boom though, and labor less valuable(reducing elite incentive to keep everybody alive), I'm unsure it won't change again. Peter Thiel and now Vance seem pretty adjacent to some bizarre and disturbing philosophers that support some weird capital-feudalism.