As Thrawn pointed out, Crimson Empire is part of the actual "lineage" of the main Empire. If you read the Era 3 News Post, that explains exactly how they're playable.
I mean our god emperor said it was highly unlikely for zero command but my counter argument is the dushkan league are minor as hell and we still got atleast 1 GC with them (sadly no hapan GC)
Factions don't get GCs, events get GCs. The closest thing we have to an exception for this is The Stars Align, since we wanted another small GC. The Duskhan League are minor, yes. They were, however, incredibly relevant to the Black Fleet Crisis, considering they were one of two participants. The Hapans are present for Hunt for Zsinj, which is where they were a prominent player, as well as the progressive GCs. Zero Command has no similar campaign except Reunification, where they are present as one group amongst many. Having a two faction GC like that means it makes sense for both sides to be playable, whereas in every GC where Zero Command is present, they're both minor and one Imperial group amongst many. Since they're already playable and fleshed out for Black Fleet Crisis, the DL is at least partially justified in being playable when present in other GCs (Art/Essence type GCs). Zero Command would be, as Slornie pointed out, just another Imperial faction among a half-dozen. And just to reinforce what Slornie said, when we say that we don't just mean "derived from the Empire," we're talking about what actually comprises the faction. The Empire of the Hand came from the Empire and the Chiss, yes, however they have their own stuff going for them. The New Republic also came from the Empire. The Duskhan League may not be Imperial in the same sense (although they did come from the Empire, too), but their roster is entirely Imperial except the Trifoils and Thrustships.
What you really need to grasp here is priorities. Just wanting something in the mod doesn't mean we flip some switch and there it is. I'm sure a lot of people would love it if we turned around tomorrow and just said "guess what, Zero Command is playable," but we have a limited amount of resources and we have to determine the best way to use them. In this release, we're already working on 3 new playable factions, finishing off some stuff for the Empire of the Hand, and putting in at least a half-dozen non-playable factions. We have to choose which things give us the best options, and the most return on our work. There's plenty of stuff we'd still love to have done but simply can't make the cut for 2.2 because of time constraints, all of which is more worthwhile than a 7th faction with an assortment of Star Destroyers. Each of the factions we have presents opportunities as a crucial element or
the focal point of at least one major conflict, or controlled so much territory/military power that it warrants their inclusion on its own.
Remnant / New Republic - Obvious.
Warlord Zsinj - Hunt for Zsinj, impetus for a lot of decisions in the Bacta War.
Greater Maldrood - Post-Zsinj campaign, border wars wth Zsinj.
Eriadu Authority - First major enemy of the New Republic, Western Reaches campaign (currently not its own GC, but the primary focus of Endor Aftermath).
Pentastar Alignment - Significant territory, didn't get itself involved in early wars but was a significant player in Shadow Hand and surrounding campaigns. Lack of involvement was by deliberate choice to build up for conflict, as opposed to lack of resources (contrast with Harrsk, who had to leave ships abandoned because he couldn't crew them)
Duskhan League - The Black Fleet Crisis was entirely about them.
Empire of the Hand - Huge territory, have lots of opportunities with them which we haven't been able to explore yet.
When you look at Zero Command, they're always tiny and they're never the big bad du jour. What opportunities do they present us? What reason do we have to make them playable when even their entire roster is stuff you can get from somewhere else in the first place? Even something like the Corporate Sector Authority gives us more options. Maybe someday when we're not focused on what's actually necessary to best represent the galactic situation at different times, it'll be worth the time to flesh them out as a playable faction. Maybe even as a patch between releases. The bottom line is that the only thing they bring to the table is being able to play with something named "Zero Command," which isn't something it's worth it for us to indulge at the moment.
It's a different thing with the Ssi-Ruuvi. We'd absolutely love to have them, they present MUCH better opportunities than Zero Command ever will. Just the fact that we know they have dinosaurs with guns doesn't mean they have an actual ground roster, since a faction can't really rely on just infantry in a game like EaW, and the big thing here is
we have to actually make them, which takes A LOT of time and resources. Considering how little they're actually fleshed out, especially on ground, even they would likely only be a non-playable.