I've said this before on other boards here, but the thing is that UPN wanted them used as primary foes because the audience hated EVERY SINGLE other Alien race VOY ever created as an antagonist. Not as some background element, as an upfront enemy.
That's because all their other antagonists were incredibly lame. The only ones with any clout were the Vidiians because it was a passingly interesting and new idea, and even they had limited uses. What they needed was some decent antagonists of their
own.
And like I said, every single time they tried the fan reaction was nothing but hatred. They were ready to rip into anything new VOY tried before it even aired, because all they wanted were the same aliens from the prior shows. DS9 pulled it off with the Dominion because they were allowed to be more serialized and blended it with plenty of stories with the familiar races.
Whenever VOY encountered AQ species, it seemed contrived and implausible to me. Heck, it even got to the point where nobody onboard the ship even noticed (remember the Bajoran Marika in "Survival Instinct" wandering around Voyager without anyone blinking an eye?), esp given that this is a Trek universe where our characters can immediately distinguish identical-looking species.
Voyager also made me realize how littered the DQ must be with Earth-related crap, esp considering how much Voyager discovered compared to amt of space explored (The 37's, The Raven, Friendship One, Scorpion, Dark Frontier, Unity, Equinox, and Distant Origin come to mind immediately). But the whole Earth-centered galaxy is one of my bigger Trek complaints in general.
The fan dislike arose when it was consistently and unwaiveringly mediocre while DS9 got its ass in gear.
Not to mention that Voyager threw the entire premise of the show out the window, showing very little recognition to their situation (never ending torpedoes and shuttle craft) or even in-universe consistency (constant dialogue errors in distance traveled, never reaching the BQ, and not being able to locate Mezoti's people (Norcadians) despite visiting Norcadia Prime in the previous episode "Tsunkatse")
This caused them to drop said races before they could be developed into anything better, leaving only the Borg who had already been established as a threat in other series.
True, but considering VOY's premise, the antagonist races
had to be dropped (save for time travel) to be believable, which would not be conducive to neither the writers developing a species nor an audience growing attached to a species. And if the audience ever did like a species, they'd have to be thrown out the window (amid fan grievances) rather quickly if we were to believe that Voyager was headed toward the AQ, sometimes in great leaps and bounds, and that the antagonist species did not control vast amounts of space (although it kind of worked with the nomadic Hirogen).