Well, sure ever lower rated episode has someone who likes it, just as there are people who like movies like TFF or Nemesis or even the lower tiered series like Voyager, Enterprise or Disco.
Lower tier? Voyager?
Popularity isn't only measured by people watching. It's also measured by how they engage with it in other ways.
For example, this is a screenshot I just took of the basic stats of the number of Star Trek stories published on fanfiction.net:
Note which series outranks TNG by more than two to one. It's Voyager.
VOYAGER has The Most Stories of all of them. They range from short drabbles to stories that have been going on for years, and the chapters number well over a hundred. There's everything from humor to adventure to some that explore some very serious ethical ideas.
That's a sign of an engaged fandom, and fanfic writers don't do it for money, like the professional authors do. They do it because they love the show and have a story to tell.
I feel like I can find good in every episode. Spocks Brain and Threshold might not be regarded highly, but I think the first halves of both episodes were actually good. SB had the meeting on the bridge, and Threshold had an interesting premise of could the Voyager crew get home if Warp 10 was perfected.
Threshold... I spent time recently searching out fanfic related to that episode. It doesn't make me like it any more than I did before (which is to say I really don't like it at all), but to its credit it has spurred some people to discuss the ethics of child abandonment (yes, that's what the crew is guilty of, leaving Paris and Janeway's offspring behind on that planet).
Probably.
In my experience, not just regarding STAR TREK, nothing is so obscure or forgettable that somebody doesn't love it dearly, if only because they imprinted on it at an impressionable age or because it got them through a difficult time.
I'm reminded of Robert Silverberg's novel,
Up the Line, and I haven't forgotten that novel you co-authored in that setting. I'm part of Silverberg's email group (he doesn't like social media, so leaves that to others), and if memory serves, he announced a couple of years ago that Up the Line had been optioned.
Of course that doesn't mean a movie or series will actually get made, and they'd have to change a couple of things. It's precisely the sexist attitudes of some of the characters that prompted some of the ladies in my old Time Travel Novels group on Yahoo to give a massive thumbs-down to Silverberg's book. I told them yes, these characters' attitudes aren't great. But that doesn't mean Silverberg himself has those attitudes (he definitely doesn't). I asked them to please just consider the time travel concepts used in the book and read to the end - and it's such a WTF? ending that it really gives the engaged reader a reaction they likely didn't expect to have.
Anyway, this particular novel is one of my favorites, I'm fully aware that some people have very valid reasons for disliking it, and I don't care. I love the concept of time tourism, and the crazy shenanigans and problems people can get into or cause by not being careful. It's also what helped me decide on my SCA persona's backstory, and to take an interest in Byzantine history.
So people who like some unpopular Star Trek stories may actually like them for reasons other than the ones generally expected. It may seem baffling, but whatever. For instance, I'm not a person who likes the plot of "Sub Rosa" and have never liked Beverly Crusher. But I am a fan of Duncan Regehr, so this episode is one I'll watch.
Voyager is not "lower-tier" Trek. In fact, I'd wager it's the most popular series after TNG for modern audiences.
Well, it's certainly the most popular choice for fanfiction, at least on one site (haven't checked the other major sites).