Second that. Also, they have the advantage that there's a thousand (nominally) chapters, and most are undescribed. Loads of players make up their own (or take one that's almost totally undefined). Of course, you can do that with hundreds of Codex chapters identical but for their names and colour schemes.maglag wrote:So of course GW does a zillion sphech merines spin-offs because they will sell.
Imperial factions are going to be popular because they are (mostly) human, which most players and most history is about. Sure, you can do your Ancient Egypt in space aliens, but if you want to do almost any other time period you need to do Marines or Guard or something. Each of the IG regiments GW sold models for was based on a real military at some point in history.
Now, making them all different is difficult, though actually producing models for them shouldn't be. Middenheim mercenaries were human mercenaries that also used the "hairy heads" sprue bits, and that was 20 years ago. Take standard kits and choose an upgrade kit.
As for allies, way back when "up to 25% of your points can be from a list of allies" was a thing, and to make it fair, evil armies could take other evil armies as allies, even if there wasn't much fluff connection. Not perfect, but better.