Why an early Iwo Jima landing creates an unnecessary risk

What if Nimitz bypassed the Palaus and sent the 1st Marine Division to Iwo Jima in September 1944?

It could bring bomber support forward sooner, but sustaining the operation with the Philippines still behind it creates a risk the United States did not need to take.

An earlier landing could bring bomber support closer to Japan if the island could be supplied and held. The scenario leaves the Philippines unsecured behind the new position, adding a sustainment problem to the landing itself. The judgment here is that this creates an avoidable operational risk. Any gain in bombing access has to be weighed against the ability to support an exposed foothold.