Even if government authorities were not subject to special-interest influence, they would have less motivation to conserve wisely than speculators do. If bureaucrats make wasteful decisions, their salaries aren't reduced. Indeed, their failures often result in larger budgets, supposedly so they can do a better job. If speculators don't conserve enough they pass up profitable opportunities to buy low and sell high, and if they conserve too much they lose money by buying high and selling low. As opposed to bureaucrats, who can survive despite their mistakes, the speculator who consistently makes mistakes is soon relieved of the money necessary to continue speculating.
Speculators can also act much more quickly than any government agency.
For example, at the first indication that next year's Brazilian coffee crop will be devastated by a frost, speculators will immediately purchase raw coffee beans to store them until next year. Consumers will still see plenty of ground coffee in the stores, but suddenly the prices will be higher. What consumers don't see is that coffee prices will be lower next year than they otherwise would have been because they are higher today, and that their reduced consumption today will be more than compensated by their greater consumption later. The complaint will be that greedy speculators have unnecessarily driven up prices. Interestingly, the universal complaint against speculators that they cause current prices to be too high is really a complaint that they conserve too much.