Earlier quoted context omitted.
what if the fun for them is the game engine? because game devs are customers too, it's technical product dev.
their stated goal is to become a self-sustaining indie game dev. They fail because instead of shipping a game they spent time making an engine and then running out of funds an having to get job not making their own stuff. If their stated goal was to make a game engine then sure. That wasn't their stated goal.
i see. thanks for the context.