part of the definition of theft is that the original owner is deprived of it, which does not apply to copyright infringement.
You can only argue with damages from the perspective of potential profits, still not theft though.
I think you're wrong: there is absolutely damage to the authors and publishers from what the AI companies have done.
Or with services, if a barber cuts your hair and then you run away without paying them, do you not consider that theft, even though there's no change in ownership occurring?