the main reason ds9 isn't remembered as well as the original series or tng by the general populace is not just because it wasn't the very first trek or the most popular trek (tng's popularity was what really brought trek into the mainstream).
it was hated by Rick Berman, who was the head of the franchise at its height, and who deliberately spited it by never including its canon in other treks.
and that effect has lasted to this day, as modern writers who only bother to watch Star Trek movies never seem to remember ds9 even exists. the way the Pine-Quinto movies mention Archer and his beagle, and trek movies and shows make multiple references to TOS, and newer treks center entirely around tng plots or the Borg.
the way they brought back seven of nine before literally anyone on the cast of ds9.
there's a reason that the damn tng movies had a million references to Voyager, with Janeway and the EMH actually having cameos, but ds9 never even got a passing reference, even where it actually would've been appropriate.
Berman hated ds9 for its focus on serialization, i. e., connected storytelling, rather than syndication, i. e. episodic storytelling, because he was a money grubbing misogynist and homophobe, who thought all the money was in syndication. he hated the writers/other producers of ds9 for going behind his back and doing their damnedest to make quality star trek.
one of my favorite spiteful Berman stories is that in star trek first contact, the 2nd tng movie, he wanted to blow up the defiant and destroy it permanently, just for no reason at all.
and the ds9 writers were upset because no one had asked them about it. so they said you can destroy the defiant, but we're just gonna keep using the defiant and pretending it didn't blow up if you do.
which is why Worf asks Picard, in a completely thrown in line, what's the status of the defiant, and Picard says adrift, but salvageable.
and this particular movie is funny to me also because in that period, Worf is technically supposed to still be serving on ds9, and bringing him into the movie was basically justified as something of a side quest for him, being dragged off the station for a little tng romp.
so you see the crew of the defiant, but... again. Berman spite. rather than letting ANYONE on ds9 cameo in the first contact movie, even though that might've been cool... they just have some randos. one might be Adam Scott.
and remember that JANEWAY AND THE EMH are in that movie.
so berman deliberately wanted to spite ds9 by destroying the defiant, stealing worf (even making fun of him for his role on ds9 in another thrown in riker line) AND snub the entire crew of ds9 by having none of them anywhere in the movie, even though they COULD HAVE CAMEOED TOO, or at least been mentioned...
and to me that's pretty funny, because Rick Berman could have as many tantrums as he wanted behind closed doors, and hate the staff of ds9.
didn't make a difference. they'd still keep defying him, and you know...
not to be a total prick but... ds9 still has a thriving fanbase to this day. tng does too, and so does tos, and star trek in general is doing pretty well...
but out of all the old treks, ds9 has aged the best, not just in how it looks, but also in how it bridges the gap between, old world optimistic charm and more gritty, humanistic sci fi story telling.
it balanced syndication and serialization really well, and had great standalone episodes AND a fun connecting overarching narrative that made the world of star trek feel richer and more lived in. I also want to say that for modern audiences, who are accustomed to serialization more than syndication, ds9 is a far easier entry point into the world of star trek than any other trek.
Rick Berman can go fuck himself, is what I'm saying, in summation.
ds9 will stand the test of time.
both tng and voy succeeded in spite of Berman. not because of him. everything that makes those two shows work, is in defiance of the Roddenberry mandates that both Roddenberry and Berman constantly tried to uphold, even though it was to the detriment of the stories.