As I am sure many of you are aware, there is a sentiment within the 40k community where people denigrate the Chaos Primarchs for essentially doing nothing for 10,000 years. I don't get it. Maybe it is just a stupid meme, but these folks seem to gripe about Mortarion or Lorgar like they are particularly inept heads of state, rather than made up super-humans-turned-daemon. Sure, it seems a little boring that they sit on their infernal worlds rather than reaving across the weakling Imperium... but that is just how Geedubs wanted it. Don't blame the fictional entity for its masters allowing it to languish. After all, these godlike beings were intentionally sidelined by GW for thousands of years, and for some fairly legitimate reasons. For starters, there is the fact that Primarchs were supposed to be legendary backdrop characters, heroes and monsters whose actions saved or damned their sons... and GW was happy with that. There were a few rare forays, a few spurts of activity; Angron got involved in a few sector-wide bloodbaths, but that was the exception, not the rule. Primarch involvement in 40k was basically unheard of for most of the game's history. And that makes sense. When a significant part of your story involves war in heaven scenario between expys of God, the Angels, and the Devil (roughly speaking), you end up with some dang powerful entities running around. Lords of War/Apocalypse scale units have only relatively recently become fair play in 'normal' games. I can't imagine something with a Primarch's statline floating around in 4th ed... well, I can, Angron had published stats, but the dude had a whole pack of bloodthirsters as 'bodyguards.' No one fielded Angron on the regular. Furthermore, GW didn't have models for them. That hasn't stopped GW before, necessarily (see Angron, above), but they clearly weren't interested in making or seriously supporting Primarchs in 40k for general 40k. Hard to get people hyped about Blood Angel releases when your stories center around daemon Primarchs taking the colons of everyone in their path. There is also the glaring absence of loyalist Primarchs that poses a bit of a problem, both from a consumer standpoint and a thematic one. If daemon Primarchs are out there, rampaging around, taking bubblegum and chewing names, things would have been kind of out of whack. The Primarchs are presented as demi-gods, the paragons of their kind and a sort of end-all-be-all for Astartes forces. If the chaos players get super daemon space marines, there needs to be suitable opposition on the Imperial side (and no, Draigo doesn't cut it). If I were an Imperial player, I would feel distinctly left out... heck, the fact we Chaos players have two Primarchs and loyalists only have one already has lots of folks pining and speculating. tl;dr, daemon Primarchs were constrained in the fluff for a bunch of meta reasons, rather than 'in-universe' ones. They only 'lazy' ones here are GW, for failing to come up with a satisfactory story explanation that exclude them from the game.