Why are they limited to certain factions?

Shouldn't all factions be able to recruit regionals in an area? They don't rely on any factional training or anything, so I would think that they should be available to anyone who controls a certain territory. This would add a lot of diversity, and make certain territories very attractive for the player. Why would a Romanii Player ordinarily conquer Britania? Not much reason to, but if they can access all the Goidilic units there would be a lot of incentive to get those nice units.

I also wanted to know if the EB team was considering moving mercenaries to the regional MICs, since that would solve the Merc Spamming generals and make them retrainable. You'd also get a lot more unit cards, or spaces (or whatever they're called), since you wouldn't have to have a space for the merc and one for the regional. This way regionally recruited Pezhetairoi and Mercenary Pezhetairoi are the same thing. Saves space and makes sense. It would also allow for more units for lesser factions (like Hayasdan/Pontos) and more regionals.