There's nothing at all weird or inconsistent about that. The amp is a monitor for me. I want to be able to control how loud my personal monitor volume without affecting the FOH. I can't imagine tying the DI volume to the master volume being of benefit to either the bassist or the FOH engineer.
I first realized that my old M9 had a post master DI on a gig. I thought there was something wrong with it. I still do.

But in any case, I had it modified to be pre-master. I also had the volume taper changed to be more linear, both of which made the amp infinitely more usable for me. By the way, Mesa consulted with the local shop for these mods, and even they didn't seem to have a justification for the post-master thing. @agedhorse ?