Tradition. Since the Romans, running bond has been the chosen method of block or stone construction. Vertical is quicker under most circumstances. Although switching to 8" panels may cut that advantage down.

Thanks Smartwall. I've seen many of your contributions to this forum. That makes a lot of sense. Even if the core is solid you still have to build the form and building HORT is what they have been doing for a very long time.

In my research I thought the minimal bracing requirements for a HORT wall would be a big draw, especially for a DIY project, but now I'm second guessing that idea. If you are pouring a 8-10 ft wall having the bracing probably goes a long way for piece of mind. You get one shot to get it right. I guess since the bracing also acts as a scaffolding its a bonus for the pouring and placing hardware.

in horizontal the cut offs can be reused. They can be reused both in height change instances and horizontally in corners and around windows.

Vertical is cut off and not of real use? I have never done vert so just my opinion. Wonder if vert pushes apart more, horizontal can't push apart do to the interlocking.

Another bit of food for thought. You can actually use a standard icf block and build vertically without using a running bond system. Seems that the icf companies have overlooked this possibility. I've done it, and it saves a crap load of time.