Prospects break your heart, this is why using them as capital is usually the smart play when you have the chance. These franchises that rely on getting 3-5 extra picks every year and run a team with youth really can't get married to their prospects. They have to supplement when they can, and if they aren't willing to do that with money, they have to do it via trade.
Milwaukee is probably the only success story with this at present (rays in the past but they're sliding) and they might actually be trading their front line pitchers before the deadline even if they're in contention.
These teams should be sinking every dollar they can spare into player development (the brewers clearly did) to ensure they get the most out of all their handout draft picks in the minors and trade some for bonafide big leaguers whenever they need to. Hoarding them all just doesn't pan out 9 times out of 10.