It’s more the result of there not being much demand for the entire 20 year run of Pokemon, so they didn’t bother keeping them packaged together. Otherwise they’d have priced it accordingly, and the services may not have wanted it at that price.

It’s like how classic Doctor Who and current Doctor Who weren’t packaged together: the demand for one was diff than the other, so it made sense to let streaming services only pay for the one their customers wanted most.