The benefits of soy come from a combination of the soy isoflavones and the soy protein. The safety of isoflavone capsules is not yet known. Isoflavone pills are made by chemically extracting the isoflavones from soy protein. This leaves behind many beneficial compounds found in soy and the soy protein itself. Recent studies have shown that isoflavone pills don't produce the same beneficial effects as good as whole soy does.
Soy contains thousands of compounds.
It is silly to think that a pill will work as good as the entire blend. More importantly, we don't know if isoflavone pills are safe yet. Soy is a natural food source for humans. Red clover and black cohosh are not and can produce unwanted effects. Much more safety data exists on soy.