can overlap with discrimination?

of course. is it the main reason? doubtful. the numbers alone just don't favor them. the relatively small proportions of the population who are x + also writers + also writing about these subjects = a much smaller talent pool to draw from. the odds that some of these will also be good writers with good stories...? way smaller. but yeah, it would be great to see more direct representation in the field. then...

the people publishing and producing have selected stories from the cis perspective looking in

if this is the perspective people are interested in hearing from, then what does that tell you about the difference in the narratives being shared? extrapolating from what i've personally read of 'own voices' type literature vs stories told from the outside, my take is this: the majority of the reading public is not x. they are genuinely curious and interested in the lives of x people. but if they wanted to read histories and ethnographies about those lives, they would find the non-fiction section (i often do). when they seek out literature, what they actually want are stories that frame an engaging, meaningful narrative around the lives of individual x characters, with satisfying character arcs and themes.

what the vast majority of the book-reading population is not interested in: pity porn, liberal guilt diatribes, scapegoating, and most of all, ressentiment. once you've read one or two of these, you've pretty much read them all. which is not to say they're not a worthwhile POV to consider (we should consider every POV), or that there won't be fans, just that they're not satisfying literature. no one has a 'right' to have their perspective read. and if it's unappealing, people don't have to buy it. that's not discrimination, it's just capitalism. no one is saying they can't publish it somewhere, just that probably most people aren't going to want to read it.

so, are there more stories out there from x authors that just tell good, engaging stories about interesting x characters, and address universal themes that even though i am not x i can still relate to? i hope so because, yeah, i'd love to read them. the difference, i think, comes down not to the identity of the author, but to the nature of the themes that frame the stories themselves. what are these different authors trying to convey with their different stories, and what makes one version have wide appeal (and, in the big picture, wide acceptance for and interest in x characters), and another version a total turn-off? food for thought...

instances where it’s okay for a person outside a culture to partake in some culturally significant thing while someone from that culture originally can’t do the same without facing discrimination or ridicule.

this is just NOT a thing. the example you gave is not an example of cultural appropriation or discrimination, it's an example of workplace dress codes, safety rules, and hygiene standards which apply to people of all ethnicities--it's just that certain people don't get special treatment because of their ethnicity. do you think they should? everyone is made aware before they take on a job that in order to, for example cook or operate machinery, they will have to secure loose hair, remove piercings and jewelry, wear uniforms/workplace-appropriate clothing, helmets, eye/hearing protection, etc, in compliance with company/gov't rules. those go for all employees, not just those of particular races and ethnicities, and if a white employee has hair extensions or a duck dynasty beard, the rules are the same for them (a local white chef has to wear a hairnet over his giant beard or cut it).

part of being a productive member of society means accepting that there are appropriate times and places to proudly display one's cultural preferences, and for the vast majority of us, work is not one of those places. life is about choices. i could choose to wear yoga pants every day, but i like being employed more, so i put on proper clothes. i cut my hair a certain way because i often have to wear a helmet--i value my head more than my hairstyle. i put up my hair when i work on machines or cook because i don't want to get scalped and i don't like eating hair--mine or anyone else's. i hope others are made to do likewise. this is not a hardship and it's not discrimination, it's life. people have choices to make. and it's not discrimination to ask them to make the same tough choices we all make.