Springing off of @icedragonlizard 's post about there not being a Dark Meta Knight plushie yet and why he deserves one...
...Crazy conspiracy theory here, but sometimes I feel like HAL put Dark Meta Knight in Star Allies without really thinking about the massive effect that the inclusion of the cameo Dream Friends would have on the fandom and the perception of the cast as a whole!
Like, people have already commented on how certain profiles make it sound like certain friends would be more likely to side with the Jamba Cult or just want the Jamba Heart for themselves!
But the Kirby series being the Kirby series, this suggestion of questioning loyalty faded slowly as the fandom came to warmly greet all of the friends... :cough: Susie :cough: WARMLY GREET ALL OF THE FRIENDS as Kirby's tried and true companions!
This came full circle in Merry Magoland where the park's golden statues really imply that, from the point of view of Magolor (himself implied to have seen multiple different timelines) these people are all HEROES who helped Kirby and saved the day with him!
...But then, HAL and even the fandom seemingly couldn't figure out a way to explain Dark Meta Knight's change. Even Daroach, who is almost explicitly in Star Allies to steal the Jamba Heart, was a steadfast ally in Mass Attack. It's easy enough to spin him becoming a friend. But DMK never had that moment of ally-ship. (Neither did Marx, but his heavily implied friendship with bad-guy-turned-good-guy Magolor indicates that he can at least behave.)
A few people, myself included, have worked hard to try and discover and share about DMK's heroic (?) side that could potentially earn him a place in the Star Allies! (In my verse, he's explicitly a forever unsung, uncredited hero of KatAM, mostly due to him being a terse bloodknight.) but I'm not sure HAL has decided just what he is yet.
Heck, he has NEVER had a speaking line, I don't think?!?
I don't know if this absence of additional lore means that they're still figuring out how they want to characterize Dark Meta Knight going forward or if they're all in their office sweating right now going, "Oh god!! We accidentally canonized the biggest jerk in the Kirby series as a HERO because we wanted to save on programming costs by including a palette swap Meta Knight!! How do we fix this?!?"
...But the Kirby Twitter DID make that post about DMK's ranking and the Mirror last year when Magoland was going strong, so they haven't forgotten about him. Even if they're staying characteristically... silent ...about him for now! ^_-