Why didn't the ICRC visit the coalition POWs held by Iraq?
Basically because the conflict developed very rapidly, causing a breakdown of the Iraqi chain of command; this made it impossible for the ICRC in Iraq to deal with the relevant authorities.
Before the conflict broke out the ICRC, as it always does, reminded all sides of their obligations under the Geneva Conventions, which include granting ICRC delegates access to prisoners of war and civilian internees.
As soon as the ICRC learned that coalition personnel had been taken prisoner it urgently sought access to them, approaching the authorities in Baghdad. The ICRC was told that access could be granted as soon as the POWs were transferred to the Iraqi military police. However, because of the sudden collapse of the government, it became impossible to find anyone to deal with and there was no way of knowing where any prisoners were being held. Today there are no coalition forces known to be in captivity.