Len, I actually authored the straight wall for MI in 2009 but took 5 years to pass in 2014. The issue is agencies do not want "high" power rifle in shotgun zones. We can have hours of discussion on WTHELLO are they thinking.
In MI, it was based on MI allowed straight wall in handgun so it was simply allow same in rifle configuration. OMG!!!, you would think we were asking for 50BMG! Simply a political decision on their part not based on one shred of ballistics. Finally got it through because it was universally supported by legislative representatives and NRC. The intent of this rule was hunter sustainability first and foremost. I was seeing kids back away from 20 ga slug guns at bench and thought what if 44Mag rifle? Less recoil, cheaper, accurate, rifle versus shotgun all positive for new shooters. Which led to the legislative approach. Thankfully, I had a really good one for my region.
Bottleneck cartridges implies "high" power to DNR so low power cartridges like 30/30, 35Rem, 32Spec etc will never be allowed. Politics. MIDNR does not have sportsmen and sportswomen first, politics will be first.
Please don't try to understand their position with logic, you will just open up another bottle of bourbon.