also i read the page about forking and it seems to have little relevance here. it focuses entirely on tools, that is, software which performs work. games are entirely different, because they are intended to entertain.
while the quality of a tool is subjective (see vi/emacs debate), the quality of entertainment is much more so. hence, there will be many more modifications made to games than to tools. most of the examples given on the forking page were simple chains of forks getting incorporated back into the parent, or something dying and forking into two separate projects.
now, take a look at the amount of mods minecraft has. yes, minecraft is extremely popular and has a very large modding scene, and a libre game would probably have less mods, but the point still stands. folding every mod anyone has ever made back into the main branch and putting them under menu options would be hopelessly impractical to manage and it would push source tree and binary sizes through the roof, for features that a lot of players won't even use.