“Do you know (or can you guess) why not?”
Well, if you would answer if you consider United Pentecostal Church in with charismatics? (with them espousing Oneness as their Christology )
No, I do not consider them "in with charismatics". So to keep score, you've inquired about introducing/categorizing/retrofitting the LDS, the Adventists, the Jehovah's Witnesses, and now the United Pentecostal Church into my "taxonomy".
So I'm asking again - why do you think that any/all of them weren't included before?