"True, but how does this insight explain why the physical constants in the universe favor life's existence instead of it's non-existence?"
It wasn't meant to, as Brian Harper explained. It simply observed that the only reason why this universe is special in having those fine-tuned physical constants is because there are intelligent beings around to notice the relationship. The implication is that if there were no intelligent beings then the "specialness" of this universe would go unnoticed and thus would be unremarkable. I realize that this can be a counter-intuitive concept, and as Brian pointed out it doesn't invalidate the idea of that the universe was the result of intelligent design. I was simply pointing out that evolutionists had noticed this concept before Ross had, but had found nothing particularly disturbing about it.
As for explanations, there are three. The first is the Strong Anthropic Principle, which in essence states that the need to create intelligent beings that will recognize the existence of the universe places severe constraints on the values of the physical constants. The second are the oscillating and baby universe theories, which in essence state that so many universes have existed or do exist that by sheer dumb luck one would have the right values for the physical constants to create life. The third is that for any viable universe to exist at all the values of the physical constants would have to be similar to those that produce life; in other words, that any departure in any of the values from that necessary for life would make the chance of a universe existing at all slim to impossible.
"The universe is not a replicating system so unless the only universe that exists supports life there will never be a subsequent universe that supports life."
That assumes that this is the only universe that has ever existed or that could ever exist, and thus must have a purpose to it. In point of fact, we simply cannot say that because we have no way of knowing