Probably the greatest difficulty in film manufacturing would be the correct layering of the emulsion. That step has to be pretty exact to gain full reproducibility and quality control. Another problem is controlling the various steps in emulsion production considering the various sensitization steps and materials. Who knows the exact kind and quantity of these chemicals used to produce the various effects we see in modern (and classic) films? Trade secrets! Even the times and temperatures used in processing emulsions are closely guarded secrets even today. Unless one wants to wing it as a hobby there are EPA ad OSHA requirements. Film manufacturing involves a lot of solvents and some by-products that could be problematic. Yes, one can do it but I’d rather pay more to get a quality product ready for use.
I believe that someone somewhere will continue to make at least b&w films for ever. The cost may be high and the quality control less than that of the present BIG BOYS, but as there will always be a need, there will be a supply.