They're all burning billions to incrementally one-up each other with no hope of these investments ever paying off since models are interchangeable and have no moat. They're trying to get regulators to step in and force a pause.
However, we know that users frequently switch models/providers, and that models stay relevant for (increasingly) short periods release. I don't know what the training costs are, but I bet they're very substantial.
"if they stop training" is exactly the point I'm making. They can't stop training if the competition is still training.