Retrofitting games with accessibility options can, to your point, be expensive. However, games can be designed to be inclusive as we're going along e.g, considering minimum text sizes when building HUDs, ensuring mechanics communicate info with multiple methods of feedback, etc
I'd also like to add that, in many cases the benefits outweigh the cost even in the case of retrofitting. From a cost case, studies suggest that disabled people are highly represented in the gaming community & personally I just think its neat that more people can play! :-)