You are correct but so is the parent of your post, the key term they used is "generally" and I would say that is a correct observation. General problem libraries tend to not sell. There are specialty markets where one can make money from licencing libraries or frameworks as you highlighted game/cinematic there is also some areas in medical and legal but for the most part if one is building a general purpose library or one that appeals to a broad market, they tend to not be commercially viable. Those that provide specific solutions for a vertical tend to have more success in commercial licencing.