They tried repeatedly to create alien species that could be used in recurring roles. The Kazon, the Vidiians, the Krenim, the Hirogen, etc. The audience didn't like a single one of them and continually pointed out how it didn't make sense how a constantly moving ship shouldn't have recurring enemies.
What makes you think these robots would work out any better than any of those others? The audience already made it perfectly clear they didn't want any new aliens to begin with.
DS9 was able to use the Dominion through out the run of the show, how many people thought the Dominion were lame villains?
The problem with a lot of the Voyager created villains, many of them were not memorable or menacing or interesting and felt like cheap knocks off other villains. If the Kazon are just the poor man's Klingons, why should I care about them? At least the robots could have been a unique enemy species in Star Trek lore.