You act like you can change balls while your playing real golf or something weird like that...
I imagine that once you start a game that the programming is all set and can not be changed or something like that. But its still stupid not to be able to pick one of the stray,better balls in your bag than resort back to the unlimited.
but it may have something to do with the water holes and hazards that I or everyone else would change to a cheaper ball just in case, then switch back to a better ball once on the green.Therefore making your better balls last longer and not having to buy them quite as often....