In 12c, why does user oracle need to be a member of asmdba?

This is not a "how to" question, but more of a "why is ASM designed the way it is question":

Recently, as in 12c databases, I have been noticing that the ASM diskgroups are not visible to the rdbms owner (oracle) unless it is a member of the asmdba group. For example I install grid infrastructure (GI) as user grid, and grid is a member of asmdba. The user grid has ownership of all diskgroups, and each diskgroup has volumes that have permissions (RHEL7) that look like this: brw-rw----. 1 root asmdba 202,  96 Aug 27 22:19 /dev/xvdg

I usually install the database as user oracle, so I use dbca, here I notice that unless oracle is a member of asmdba, I can't see the diskgroups from within dbca, so I make oracle a member of asmdba, now I can see the diskgroups, DATA, FRA, REDO, etc. so the install was done and it works.