We are repeatedly assured that we need "diverse" characters (of uniform belief) so that women, and other minorities than while males (women are not a minority) can see themselves in the characters to better appreciate the story and the role model.
I'm going to ignore for the moment the whole "content of character" not being the same as "color of skin/shape of genitals" thing, and take them for their word.
If we need people who represent us - let's leave aside stories with alien protagonists, etc. that we've enjoyed, we're not dealing with reality but SJW-world - then stories who's protagonists are female will not appeal to men by the same logic that male protagonists supposedly don't appeal to women.
If stories with white protagonists cannot be understood or appreciated by blacks, then, in the US, writing a black protagonist excludes roughly 80% or more of the population.
If stories with straight characters cannot be appreciated by gay people, then the inverse is that the 90+% of the world, more likely 97+%, that isn't LGBTBBQWHATEVER will never appreciate it or gain insight from it.
Instead of believing in a universal human experience that can be, at times, touched even by people who don't share them, we instead eliminate large swathes of the potential market (and if you argue that straight people can appreciate LGwhatever-protag fiction, what's the problem with the opposite, again?).
As I mentioned with computers - in this day and age, and even with the gatekeepers given how eager they were for the "correct" kinds of authors and views, the only thing keeping "minorities" and minorities from publishing to their available audience, even if you agree on it being so self-limiting, is their own desire to do so.
But if you buy this "must be representative" drivel, and a publisher can only put out , say, 20 books a year, even if the percentage of minorities enjoying SF were the same as for the bemoaned "white men" demographic, then every book published targeting 10% or less of the available audience will exclude everyone else who doesn't fit, and not sell as well.
And then they wonder why the market share for SJW-themed comics and books is falling off a cliff.