IP theft involves deprivation of the holder of ownership claim. Observing a game before making your own game, listening to music before releasing your own track, viewing photos before making a go at the same composition, do not do that. Claiming them as your own, however, does do that. Using them to train a (commercial) system that allows anybody to recreate them and claim as your own does do that.
It is, actually, more of a problem than theft of physical items. The latter you can just buy again while the former robs you of intangible values that among other things may grant you the ability to just buy physical property. The latter doesn’t scale and is generally more difficult because it’s more visible, while the former can be (and is being, in fact) done at population scale without people realizing it until it’s too late. Also, expectation of ownership claim is a meta level of why people want to make more original things, including new and cool physical items.
It is, actually, more of a problem than theft of physical items. The latter you can just buy again while the former robs you of intangible values that among other things may grant you the ability to just buy physical property. The latter doesn’t scale and is generally more difficult because it’s more visible, while the former can be (and is being, in fact) done at population scale without people realizing it until it’s too late. Also, expectation of ownership claim is a meta level of why people want to make more original things, including new and cool physical items.