Why Haven't More Groups Within the Archaeplastids Developed Complex Multicellularity

Why haven't more groups within the archaeplastids developed complex multicellularity?

A) Many of the groups are recently evolved; with more time they will all evolve members with complex multicellularity.
B) Many of the groups are marine, and there are a limited number of marine niches that require complex multicellularity.
C) Evolution is not goal-oriented toward producing an end product with complex multicellularity; each group is successful with its current morphology.
D) Only the most diverse groups have enough species so that complex multicellularity can evolve.