Runs are more scarce than outs.
Think about it this way.. let's say every inning that you got a man on with zero or one outs, you could small ball your way to a run... Assuming you had a decent pitching staff, you'd run away with the division every year.
Obviously, a hit is more desirable than a SF, but a SF is productive.
Sure, a SF reduces the chance of a big inning, but it gets a run home. Unless you are losing by a large number of runs (in which case the win expectancy is tiny anyhow), you always will trade one out for a run. Heck, many situations it's worth trading 2 outs for a run (bunt and sac fly).