First: At-cost is certainly possible! Free might be, but there also lots of other things we need to spend our limited resources on as a society. Some of them definitely higher on the list than AI access.

But it would require finding a different way of funding future research and development. This is already partly covered by government-funded research, but that doesn’t necessarily cover the whole route to making AI actually usable and available to the public.

Second: There’s a seriously large difference in cost between using a trained AI model (such as ChatGPT) and training it in the first place. The second would be far more costly to make available for free (orders of magnitude, really). But without it, possible innovations from making AI available for free would be far more limited.