> Why are relationships, identities, trauma, and oppression trivial ideas?
That's just, my opinion. :-)
It's difficult to explain if you, with access to the entire corpus of literature humans have published until now, and having read 10, 20, 50, 100 or more of past and current books, don't already know why.
It's impossible to explain if those are the things you already think are most important.
One way — and there are many others — to think about it is to ask: what can I use these ideas in this book to build that will advance humanity? Another is: what is new about what this author is saying that hasn't already been said by anyone in the past?
> Why do you think these authors cannot hold conflicting views in their mind?
This one is more simple (but you can probably invent a better method here as well): Read any recent award winning book that "interrogates identity" (or pick another MFA blurb descriptor) then write down what you think the author's values are. Often enough, if you simply take the view that the author's values are slightly or completely mistaken, the entire novel ceases to have a purpose.
Holding a conflicting view in my mind means being able to wholeheartedly (and at least, while writing) believe that my fundamental values and assumptions about the world are wrong.
p.s. Another reply to your comment also explained it rather nicely.