Big assignments come with scrutiny. Scrutiny kills good ideas before they get a chance to prove themselves to be good ideas.
Small assignments mean fewer scrutinizers.
A good idea can be hatched for a small assignment away from the death-dealing effects of scrutiny. Get produced. Discovered. And become the big campaign.
Small assignments are like acorns. They can grow into oak trees. But a big hunk of oak stuck into the ground will always only be a big hunk of oak. Stuck in the ground.