I know a lot of developers say they want to make games, and end up making engines instead, or vice versa. So, I've been reading the minetest forums (and not playing the game) and I think about engines, and how they are designed to be used by multiple games but if the engine is too inflexible, then you can't make the type of game you want on it, on the other hand, if it is to flexible, then it is hard to mod, and newbie users don't like struggling to make games for it.
I'm also not exactly sure how engines are different from straight up forking, ie you take the code, and take it entirely in a different direction ie, an easy game for newbies with cute graphics turned into a hardcore game with realistic graphics (or vice versa)