Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
To grow, to add tissue, the plants need more fertilizer.
To maintain, the plants are still growing new leaves and discarding old leaves, but the slow growing plants you list can get by on very little fertilizer, perhaps just the amount they will get from the food you are feeding the shrimp.
As noted, light and carbon also play a role. Dose very low levels of the carbon supplement, adjust the lights correctly, and the plants should grow slowly.