If you mean the less-fun-to-work-with part, it's fairly obvious. You have a good idea, but the smarter person A has already thought about it (and rejected it after having a better idea). You manage to make a useful contribution, and it is immediately generalized and improved upon by the smarter persons B and C. It's like playing a game where you have almost no control over the outcome. This problem seems related to competence and autonomy, which are two of the three basic needs involved in intrinsic motivation.

If you mean the issue of why fun is valued more than doing something that matters, it is less clear. My guess is that's because boredom is a more immediate and pressing concern than meaningless existence (where "something that matters" is a cure for meaningless existence, and "fun" is a cure for boredom). Smart people also seem to get bored more easily, so the need to get away from boredom is probably more important for them.