Let us just look at this from a less emotive point of view.
Square Enix never expected XV to be a massive success. And it was. They didn't think there would be enough motivation to continue the DLC beyond its initial run, but there was. And this announcement wasn't based specifically on fan feedback or "malice", but on internal structural changes based on the foundation of Luminous Productions, which I think is their first dedicated subsidiary since The Game Designer Studio that created the first Crystal Chronicles.
The Luminous Productions team has apparently been working on both this mysterious new AAA title and XV itself, so they've been split between two duties for the best part of a year. Now SQEX and Luminous Productions has decided to focus its efforts on the new project, which means lower priority stuff which would eat up resources must be put aside or given a different outlet; this meant the end of a set of DLCs that were never planned, took low priority, and were frankly less anticipated than Episode Ardyn is. It also includes the PC version of the standalone Comrades apparently.
Also, this "outlet" for the DLC story needn't be anything related to XV at all. They said that they wanted something to show the kind of story they had. If it's an OVA or something, I'm not that bothered. But alternately could mean they're taking the basic narrative planned for this (which as
@Ikkin has pointed out could potentially break the lore and themes) and turning it into a whole new game unencumbered by XV's "reputation" (which is notorious at best and toxic at worst).
And as for Tabata leaving, I can't say I'm surprised. He's dedicated nearly eight years to this highly troublesome project, and I wouldn't be at all surprised if the parting was quite amicable and based on a wish to take his next project at his own pace (likely at his own studio or new division
based on his wording).
But now I will conclude with saying something I've been thinking for the best part of a year:...... I'M SICK AND TIRED OF XV, AND REALLY WANT FINAL FANTASY XVI. There. It's out.