I think this all happens mostly due to the stress trans people are inadvertently causing their parents. When your kid comes out of the closet, this will happen to a parent regardless of how liberal-minded they are. Even if you have no problem with the concept, your kid being trans brings about new kinds of threat scenarios you never had to think about before. If you’re a sensible, smart and handsome person like I truly fucking am, you can process it in a few years and come out as not being a 100% asshole towards the issue.
I feel like it’s more the opposite problem. For the parents, trans people are a vague boogeyman. They’ve never meant a trans person personally, and they’re constantly told that trans people are just waiting to jump them in the bathroom, or at sports, or all sorts of other things, so they’ve never had to contend with someone they know being trans.
If it was simply stress or threat to the kid, it wouldn’t really explain the reaction to disowning them, since most of those aren’t about the treatment that their kids would receive for being trans.
Even then, Trek hasn’t really pushed the boundaries for a good long time. When it hit it big by TNG/TOS Syndication, it ended up being the cash cow, and thus not worth risking for such controversial things.
At most, it’s just been nudging the norm, but the kind of radical shove that TOS had, and nearly got it pulled off the air twice is basically nowhere to be found.
At most, we got one or two token characters or plots, but a lot of it is mostly the norm, or just a little ahead of it.
Compare it to something less established and free to take on more risk, like the Orville. Since it doesn’t have the big brand that networks want to keep reaping without sowing, it gets a lot of flexibility Trek doesn’t really have any more.