That is easilty explained. People who are obese but not insulin resistant have a favourable fat disposition. The fat is tucked away at non dangerous places, compared to people with type 2 diabetes genetics, they get their fat stored at poor places,liver pancreas and organs.
This is a swedish youtube video about a swedish company specializing in scanning people for where their fat is located.
If you stop at 1:05 in the video, you will see an example where they compare a pair of female monozygotic twins.
Women 1. has a weight of 94kg a bmi of 34 and a waist of 103cm.
Women 2. has a weight of 109 kg a bmi of 39 and a waist size of 112cm.
The strange thing is this, the first women which seemingly have the better markers,has a liverfat percentage of 5.2 %, But the second women has a liverfat of 1.8 %.
So genetics but also lifestyle matters.
People who smoke get more viscerfal fat than others, and it is probably something to do with toxins in cigarettes,and activity also matters.