IMHO, I would only change one word in your above argument, and I would agree: "it is ideally built for the gratification of the players." I don't think that it is explicitly built for the gratification of the players as a hard and fast rule or always the case. We are talking about the subtle difference between the should and the is or the ideal and the common praxis.I'm not going to pretend there is no self-gratification the original building process, but it is also explicitly built for the gratification of the players, both in providing them discovery of the sort of things that they enjoy discovering, and to pointedly provide circumstances, scenarios, and opportunities for the players to explore their characters, especially the facets that are added in the course of play. If it is only full of things that I alone enjoy, I haven't done my job.
I say this because I have unfortunately played in far too many homebrews that felt like they were created more for the GM's self-gratification than anyone else's gratification at the table. I'm sure each and every GM may have thought that they were homebrewing for the players' satisfication, but in truth it felt like were supposed to bask in the glory of the world that the GM created and heap praise upon their masterful worldbuilding.