I believe it is only because the phrase sounds better that way, and it has become the canonical form. But I partially agree, especially with the advice you som

I believe it is only because the phrase sounds better that way, and it has become the canonical form. But I partially agree, especially with the advice you sometimes see about a service of fruit juice being the same as a serving of fruit. But many whole fruits have their sugar bound up in fiber. You don't take quite the same insulin hit eating an apple as you do drinking apple juice.