OK then, I'm asking why though instead of replacing the head mod who stepped down, why this decision was made instead?
I think you are asking a fair question, although perhaps not necessary to ask it that many times xD
Ultimately I think it comes down to maintaining a standard hierarchy structure while relieving the practical issues of having a single head mod with regards to availability.
The main advantage i can think of with a standard hierarchy structure, is that final say will remain with a single person. This means that a decision can be made quickly and with finality. This type of decision making I find to be rare, but at times is necessary. I feel as though having 2 or 3 head mods is not as efficient, as ultimately a decision needs to be made.
The above type of decision making as i mentioned is rare. For all the other tasks that require head mod privileges there is no problem for a deputy mod to resolve it. This way the workload of the head mod can be split, as Miguel is limited by his activity and time zone, regardless of his commitment.
Another way to look at it, is that neither Ryuu nor CGI have previously been head mods. So perhaps this is a mechanism that can be used to prepare them for promotion to being an actual head mod. Whether that is a head mod team or as a replacement to Miguel.