mrwittwer wrote:Anybody know the reasoning behind this?
I would assume it's so they only need the one Greater Daemon entry in the
CSM book.
Daemons are only really in the list as an extra. They're included as a generic option that's deliberately underpowered compared to their more unfettered Daemon codex brethren to keep the focus on the Chaos Marines.
Given that the book is largely concerned with generic renegades rather than the specific Chaos cults, you could explain it fluff-wise as the force not being powerful enough to summon full-strength Daemons. So while they can call on Greater Daemons, they're not manifesting at full strength, with their full range of powers, and so are reduced to just striding about whacking things.
If you want full power-ed Daemons, use the Daemon codex, or wait for the Cult-specific Chaos Marine codexes.