That’s a little like saying you can compute the profitability of the energy market by looking only at the margins of gas stations. You can’t exclude all the outlays on actually acquiring the product to sell.
Models aren't static. In order for them to remain relevant, they have to be constantly retrained with new data. Plus there's a model arms race going on and which will probably continue for the foreseeable future.
Fair point - though various distilling and retraining tricks do reduce the cost quite a bit. It’s not like everyone is doing all the work they had to do from scratch, every time.
And unlike gasoline, once models are trained there is no significant ongoing production cost.