Some maps are partial or not available in portal - conquest custom

It's not just custom conquest. For example, in VTDM there's no Iwo Jima map, in FFA it's a very small segment of Iwo Jima despite the fact that nearly all the other maps available are the full size version. I was hoping to extend my snipers-only portal game to Iwo Jima but the segment that's available is all small corridors and inside. Stranded in VTDM is missing half the map, etc. etc. I'm not sure why we can't just have the full maps in every mode.