Most chemical synthesis steps produce side products. More steps means more %yield loss. If it's possible you go from A->B at 80% efficiency. If we compare this

Most chemical synthesis steps produce side products. More steps means more %yield loss. If it's possible you go from A->B at 80% efficiency. If we compare this with A->C then C->B need to be nearly twice as efficient to provide a better yield. Remember these steps include losses due to non chemical reasons. You might have issues with your reactors or transferring the solution to a new reaction chamber might incur losses, etc. In most complex organic synth situations, the full synthesis will be 8-20 steps or so, so we're talking about yields of %efficiency^x. Lowering X helps a ton. In short, the alternate route needs to be really good to justify additional steps.