I wouldn’t say capitalism is good, but the alternatives we’ve discovered so far are either unworkable or worse.

Capitalism emerged at a time when Feudalism / Manorialism was the norm. In a Feudalist society, lords owned the land, and serfs belonged to the land. Workers were required to work on the land allocated to them for their entire lives, and their children were bound to the same land. There was no incentive for anyone to innovate or improve efficiency because there was no competition.

Capitalism was an improvement on that system. At least under capitalism, workers could move to another capitalist’s factory. At least there was competition so there were incentives to improve efficiency, and maybe sometimes to improve working conditions so that workers were more willing to work in that factory. Also, at least in theory, people weren’t assigned “factory owner” and “worker” titles at birth. It was difficult, but at least possible for a worker (or group of workers) to start a new factory. And, a badly run factory could result in a factory owner becoming just a worker.

Capitalism is better than feudalism, and better than the systems that came before feudalism which were mostly slavery-based and/or violence-based (obviously there’s a lot of overlap there).

Then, there are theoretical alternatives to capitalism which don’t actually seem to work in the real world, at least on a large scale. Collectivist things sound great in theory, but in practice almost always seem to result in oligarchs or dictators taking over. Also, because economic systems and political systems are intertwined, collectivist systems without centralized decision making power are vulnerable to being invaded by neighbours who are centralized and organized. AFAIK, we’ve never seen a collectivist system able to fend off invasions and keep operating in a collectivist way.

As a result, capitalism is the best solution we’ve been able to come up with so far that takes human nature into account and is stable over hundreds of years. But, the best capitalist systems are heavily regulated ones where the accompanying political system is constantly working to reduce the power of the people who get rich via capitalism. The capitalists hate that, and want a system where they get all the power, without realizing that effectively transforms the system into a dictatorship / oligarchy, which isn’t a good system even for the capitalists. But, oh well.