The large language models are not that much better than a single artist / programmer / technical writer (in fact they are significantly worse) working for a couple of hours. Modern tools do indeed increase the productivity of workers to the extent where AI generated content is not worth it in most (all?) industries (unless you are very cheap; but then maybe your workers will organize against you).
If we want to keep the railway analogy, training an AI model in 2025 is like building a railway line in 2025 where there is already a highway, and the highway is already sufficient for the traffic it gets, and won’t require expansion in the foreseeable future.