> If A.I. can't use others copyrighted work to learn and train, why can people?

But it is allowed to use copyrighted works to train an AI - as long as it constitutes fair use. What's probably not fair use though, is to sell or flood the market with cheap works produced by a machine, if it negatively impacts the market for the original works it's trained on. Copyright laws make a distinction between humans and machines, because they're not the same thing. For example, works created solely by non-humans, whether a machine or a monkey, can't be copyrighted. According to the US copyright office, it requires "the nexus between the human mind and creative expression".