That is a vast oversimplification of a complex system.
scrubbers also can take all CO2 out and then start pulling down alk, so a skimmer can still act in a complementary role and enhance scrubber growth. Theoretically.
Because the results are not necessarily the same. There are very likely to be benefits to running a skimmer that are difficult to quantify. Similarly, there are very likely benefits of running a scrubber that are difficult to quantify. We all know that you believe in the scrubber only system, and I am not saying that a scrubber only system is bad, just that it won't necessarily work for everyone. Also there is value in diversity of filtration, for many reasons, especially with larger systems.
Your particular setup may work well for you, but that doesn't mean that everyone should do it. Also each system has its own particulars, so even close to identical duplication of a system may yield completely different results. Just ask BeanAnimal about that, he had his system running for year trucking along like clockwork and swore up and down that it was the way to go, then the tank just crashed. And he was no slouch in the reef community.