My theories, when I read this news were:
1 - Masters of all girls and DIVA 10, are a separate group. Thus, a pop group more "normal"
2 - Another new family, and be DIVA48, but does not make sense, would have four teams ... would have 12 members each, and thus might have featured in all ...
3-6 is only new dancers. What seems to be trendy, be the whole group, but only some are in the center and sing. This reminds me of a new group Happiens.
4 - As mentioned at the top ... Sayaka undergraduate and DIVA, and Sae AKB48 and Yuka and Umechan DIVA DIVA and SDN. What I do not think it's because Sae is not very new, Sayaka Umechan.
5 - Just being a sub-unit with 10 members ...
What they find it acceptable?