Karl Mikhail was Duke not Grand Duke aka Duke Mikhail Georgievich of Mecklenbourg-Strelitz.
Sorry

. There are so many of them that sometimes you just can make a mistake.
Possibly he was a sort of a bachelor like GD Dmitriy Konstantinovich happy to be a good uncle to his nieces and nephews.
Yes, it can be a good reason.
But, I don't know, well since you mentioned GD Dimitri, is there perhaps possible that GD D and D KM were homosexual? Is there in those Russian books on the Romanovs, you mentioned something written about this posibility? I'm asking this here because unfortunatly I don't have acces to many books on the metter, so, please, don't get me wrong.
Daniela